The rear main seal, or rear main bearing seal, is a gasket between the engine and the transmission of an automobile. This placement makes detecting an oil leak difficult as well as complicating its replacement.
The most common sign of a leaking rear main seal is oil spots on a driveway or garage floor where the vehicle is parked for long periods of time. Oil may leak from multiple areas of the engine, but the rear main seal is one of the most frequent sources of a leak.
Often leaking oil from a rear main seal will drip onto the vehicle's exhaust and cause smoke to come from under the car. Smoke coming out of the tailpipe is a sign that the engine is burning oil, not a leaking rear main seal.
Leaking oil acts as an adhesive on the bottom of the car. Dirt and other road debris will stick to surfaces covered with oil. An accumulation of dirt and other debris at the junction of the engine and transmission is a good indicator of a rear main seal oil leak.
