Best Rear Main Seal Leak Additive for Engine Oil Leaks

#1 · Best Overall

1. Bar's Leaks Rear Main Repair

• Weight: 1.1 lb
• Form: Liquid

Best for: Rear-main-seal focused drivers.

Why it ranks #1: Specifically targets rear main leaks, also covers timing cover and cam seals, and comes in a 16.9-ounce bottle for the engine crankcase.

Its rear-main-seal-specific formula also targets timing-cover and cam-seal leaks, giving drivers one oil additive for several common engine sealing points. Bar’s Leaks directs users to add the full bottle to the crankcase, at or between oil changes, without overfilling.

The product works by restoring seal size, flexibility, and elasticity, while additional additives address leaks in worn seals. That combination makes it relevant to age- or heat-affected seals as well as the rear main seal named in the title. It also covers timing-cover seals, cam seals, O-rings, and other gaskets, broadening its use beyond one leak location. The maker says most leaks stop within 100 miles or two days of driving; results depend on leak severity.

Skip it if you need an additive for transmissions or hydraulic systems; ATP Automotive AT-205 Re-Seal lists those applications.

A driver addressing an engine-oil leak at the rear main, timing cover, or cam seal may appreciate its targeted coverage and simple crankcase addition. It is an additive, and the stated stopping window varies with leak severity.

Listed on Amazon as: Bar's Leaks Rear Main Seal Repair, 16.9 oz

#2 · Best Multi-Bottle Pack

2. Bar's Leaks Repair 6-Pack

• Form: Liquid
• Material: Synthetic

Best for: Frequent fleet maintenance users.

Why it ranks #2: The same rear-main-focused formula also covers timing cover, cam seals, O-rings, and gaskets; this listing includes six bottles.

A six-bottle pack of Bar’s Leaks Rear Main Seal Repair gives maintenance teams multiple applications of a formula aimed specifically at rear-main leaks. It also lists timing-cover seals, cam seals, O-rings, and other gaskets, with compatibility stated for gasoline, diesel, and turbocharged vehicles.

Bar’s Leaks describes seal restoration as returning size, flexibility, and elasticity lost through engine heat and age, while other additives address leaks in worn seals. That pairing supports its use for more than a single sealing point: the listed targets include rear mains, timing covers, cam seals, O-rings, and other gaskets. The six-bottle pack suits repeated maintenance needs. Its vehicle compatibility includes gasoline, diesel, and turbocharged types, while the supplied directions for this listing do not specify a stopping timeline.

Skip it if you need only one small bottle for a single treatment; XADO Atomex is listed as a 250 ml engine-oil treatment.

This pack fits a shop, fleet, or owner who expects repeated engine-seal maintenance and wants coverage across several leak points. It is a six-bottle quantity, so a one-off repair may call for less.

Listed on Amazon as: Bar's Leaks Rear Main Seal Repair (Pack of 6)

#3 · Broadest Fluid Coverage

3. ATP Automotive AT-205

• Weight: 8 oz
• Form: Liquid
• Material: Rubber

Best for: Multi-system rubber-seal upkeep.

Why it ranks #3: The 8-ounce resealer treats engine, transmission, power steering, differential, and hydraulic systems, and is compatible with conventional and synthetic oils.

Compatibility with engine oil, ATF, gear oil, power-steering fluid, and hydraulic oil makes AT-205 useful when rubber seals need attention across several systems. Its petroleum-distillate-free formula is specified not to over-swell or break down seals, while the 8-ounce bottle suits a focused application.

AT-205 conditions rubber seals and gaskets as the fluid circulates through the operating system, so its application extends beyond engine oil to transmissions, power steering, differentials, and hydraulic systems. The manufacturer excludes brakes, an important boundary when choosing a system treatment. Its plasticizer approach addresses seals that have dried, hardened, or worn, and the product description says it is not harmful to internal bearings and components. Check the target system before adding it.

Skip it if you need a rear-main-seal-specific formula and engine-only directions; Bar’s Leaks Rear Main Seal Repair focuses on that application.

Choose AT-205 when a vehicle has rubber-seal concerns in one of its listed fluid systems and broad fluid compatibility matters. Its stated applications exclude brakes, so keep it out of brake systems.

Listed on Amazon as: ATP Automotive AT-205 Re-Seal Stops Leaks, 8 Ounce Bottle,1-Pack

#4

4. XADO Atomex Stop Leak

• Weight: 10.8 oz

Best for: Warm-engine seal treatment.

Why it ranks #4: Its engine-oil treatment is explicitly described for high-mileage use or rear main seals and is poured into warmed engine oil.

XADO Atomex calls for adding its 250 ml treatment to warmed-up engine oil, tying application to the engine’s operating temperature. Its stated purpose is to restore elasticity in sealing materials, making it relevant to drivers addressing engine-oil leakage from rubber seals or gaskets.

The product is described as a motor-oil treatment whose special components restore elasticity in sealing materials to help eliminate oil leakage. That makes the intended benefit straightforward for a high-mileage engine or a rear-main-seal concern, both named in the title. The application instruction is specific: pour the bottle into the engine oil tank after the engine reaches operating temperature. The supplied details do not list other fluid systems, so its stated scope is engine oil.

Skip it if you need listed transmission or power-steering applications; ATP Automotive AT-205 Re-Seal covers those systems as well as engine seals.

XADO suits an owner seeking an engine-oil treatment for seal elasticity, including a high-mileage or rear-main-seal concern. Its listed application is warmed engine oil; supplied details do not establish coverage for other systems.

Listed on Amazon as: XADO ATOMEX Oil Additive Stop Leak Engine – Restore Seal and Gaskets, Treatment for Car Engine High Mileage or Rear Main Seal, Best Stopper Leaks Reseal (Bottle, 250 ml)

#5

5. BlueDevil Oil Stop Leak

• Weight: 4.8 oz
• Form: Liquid
• Material: Oil

Best for: Simple engine-oil leak applications.

Why it ranks #5: This 8-ounce engine oil additive is described for gasoline and diesel engines and claims to seal seeping or dripping oil leaks.

BlueDevil’s pour-in application lets users add the 8-ounce oil treatment to the leaking component’s sump or crankcase. The product states compatibility with gasoline and diesel engines and describes a non-clogging formula, pairing straightforward application with broad engine-fuel compatibility.

The listed application is to pour the recommended amount into the leaking component’s oil sump or crankcase, which keeps the process focused on an engine-oil leak. BlueDevil says the formula is non-clogging and will not harm the engine, and its compatibility includes gasoline and diesel engines. It is promoted as a permanent seal that remains sealed after miles of driving, though the supplied details do not define a specific distance or timeline. Protective eyewear is advised during use.

Skip it if you need listed coverage for power steering and differentials; BlueDevil PRO Universal Leak Repair names both systems.

This option fits a driver seeking a pour-in treatment for an engine-oil leak in a gasoline or diesel vehicle. Its supplied application centers on the sump or crankcase rather than a range of named fluid systems.

Listed on Amazon as: BlueDevil Products 49499 Oil Stop Leak – 8 Ounce

#6

6. BlueDevil PRO Leak Repair

• Weight: 1 lb

Best for: DIY multi-system leak treatment.

Why it ranks #6: The 12-ounce formula specifically includes rear main seals, engine oil, power steering, and differentials, with a no-solids-or-fibers formulation.

BlueDevil PRO targets engine oil, power steering, differentials, and rear-main-seal leaks in one 12-ounce formula. Its pour-in application needs no special tools, while a no-solids-or-fibers formula is specified as non-clogging for internal components.

The product reconditions dried or cracked rubber seals, with the stated mechanism absorbing into a seal to soften, expand, and revitalize it. That seal-focused action applies across the listed engine-oil, power-steering, differential, and rear-main systems, making it useful when a leak is not confined to one named system. Its easy pour-in method is described for DIY use without special tools, and the formula contains no solids or fibers. The manufacturer says it works while driving.

Skip it if you need named transmission and hydraulic-fluid compatibility; ATP Automotive AT-205 Re-Seal lists both applications.

BlueDevil PRO fits a DIY user seeking one pour-in treatment for a rear-main or other listed system leak. Its stated coverage includes engine oil, power steering, and differentials, but not every fluid system.

Listed on Amazon as: BlueDevil PRO Universal Leak Repair | 12 oz.

#7

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7. ATP AT-205 2-Pack

• Weight: 0.27 g
• Form: Liquid
• Material: Rubber

Best for: Multi-fluid seal treatment supply.

Why it ranks #7: Two bottles of AT-205 offer the same broad rubber-seal treatment for engines and other systems, though the listing does not target rear mains specifically.

This two-pack of AT-205 Re-Seal pairs rubber-seal and gasket rejuvenation with compatibility across conventional and synthetic oils, ATF, gear oil, power-steering fluids, and hydraulic oil. Its petroleum-distillate-free formula is stated not to over-swell or break down seals.

AT-205’s broad fluid compatibility lets the treatment address rubber seals and gaskets in engines, transmissions, power steering, differentials, and hydraulic systems. The formula is described as fast acting and professional strength, while avoiding petroleum distillates that could over-swell or break down seals. Having two bottles gives users multiple applications or treatment needs on hand. The supplied details do not state a bottle volume per unit beyond the product title’s 8-ounce designation, nor do they provide a system-specific dose.

Skip it if you need a product whose directions explicitly give an engine-crankcase procedure; Bar’s Leaks Rear Main Seal Repair provides that guidance.

This pack fits owners or service users who need AT-205’s listed rubber-seal treatment across several fluid systems. Its broad compatibility is useful, but the supplied details do not provide a system-specific dosing instruction.

Listed on Amazon as: AT-205 Seal Leak Stopper 8 Ounce – 2 Pack

#8

8. BlueSeal Oil Stop Leak

• Weight: 8 oz
• Form: Liquid
• Material: Liquid, glycol-ether based

Best for: Gasoline and diesel seal care.

Why it ranks #8: The 8-ounce formula is intended for gasoline and diesel engines and also lists transmission, power steering, differential, and hydraulic system use.

BlueSeal’s petroleum-free, non-clogging formula is listed for both gasoline and diesel engines, giving mixed-vehicle households broad engine compatibility. It also conditions rubber seals across several fluid systems, including transmissions, power steering, differentials, rack and pinion systems, and hydraulics.

The product is intended to condition and recondition rubber seals without breaking down engine components, connecting its seal-care purpose with a non-clogging formula. Its multi-system list includes engine oil, transmissions, power-steering units, differentials, rack and pinion systems, and hydraulic systems, offering more application options than an engine-only treatment. Application is described as pouring directly into the oil sump. The 8-ounce bottle is a defined single-container amount; the supplied facts do not give a leak-stopping distance or time.

Skip it if you want an explicitly stated treatment for ATF and gear oil; ATP Automotive AT-205 Re-Seal lists both fluid types.

BlueSeal suits owners of gasoline or diesel vehicles seeking rubber-seal conditioning and broad system coverage. Its application directions specifically mention the oil sump, so use the listed instructions for the intended system.

Listed on Amazon as: BlueSeal Oil Stop Leak, Rear Main Seal Repair, Engine Oil Additive, 8 oz

#9 · Largest Bottle

9. Lucas Oil Stop Leak

• Weight: 0.92 kg

Best for: Larger-volume motor-oil treatment.

Why it ranks #9: Its one-quart bottle is compatible with petroleum, semi-synthetic, and full-synthetic motor oils, but the listing does not specifically name rear main seals.

The quart-size Lucas Oil treatment is compatible with petroleum, semi-synthetic, and full synthetic motor oils, making oil-type compatibility its clearest practical distinction. Its formula is stated to renew worn seals while avoiding harmful solvents, with additional claims around engine noise, oil consumption, and oil pressure.

Compatibility with three motor-oil types lets drivers use the treatment with petroleum, semi-synthetic, or full synthetic oil. Lucas says it renews worn seals without risk of damage or eventual corrosion, linking the product to engine leak maintenance rather than a single seal location. The quart bottle is substantially sized for motor-oil treatment use, while the supplied details do not specify an application dose. It also claims to reduce engine noise and oil consumption and raise oil pressure; these are product claims, not a stated guarantee for every engine.

Skip it if you need a rear-main-seal-specific product with stated crankcase directions; Bar’s Leaks Rear Main Seal Repair names that leak directly.

Lucas Oil suits owners wanting a larger-volume motor-oil treatment compatible with several oil types and focused on worn seals. The supplied listing does not give a dose, so that detail is a boundary to resolve before use.

Listed on Amazon as: Lucas Oil 10278 Engine Oil Stop Leak – 1 Quart

#10

10. STP High Mileage Treatment

• Weight: 15.2 oz

Best for: High-mileage engine oil support.

Why it ranks #10: This 15-ounce treatment is aimed at vehicles over 75,000 miles and rejuvenates seals, but its high-mileage oil-treatment focus is less rear-main-specific.

STP specifies this oil treatment for vehicles with more than 75,000 miles, combining seal-and-gasket rejuvenation with an anti-wear ZDDP additive. Its high-viscosity formula also creates a thick cushion between moving engine parts, bringing leak treatment and engine-oil support together.

The product targets high-mileage vehicles and uses ZDDP as an anti-wear agent, while its thick cushion between moving parts is intended to fight metal-to-metal friction. Separately, the stop-leak function aims to rejuvenate seals and gaskets and address engine leaks, noise, and smoke. That combination makes it an engine-oil treatment rather than a multi-system fluid additive. The 15-ounce bottle is the stated size; the product details do not identify a specific rear-main-seal application procedure.

Skip it if you want an additive explicitly focused on rear-main-seal leaks; Bar’s Leaks Rear Main Seal Repair names that application.

STP suits owners of higher-mileage cars seeking an engine-oil treatment that combines seal care with anti-wear support. It addresses engine leaks broadly, while the supplied information does not specify a rear-main procedure.

Listed on Amazon as: STP High Mileage Oil Treatment + Stop Leak, Improves Car Oil, 15 Fl Oz