It has been determined that 90% of all rear main seal oil leak complaints checked in the last five years are leaks in the pan gasket, rocker covers, side covers, etc., and are not leaking rear main oil seals.
The following is a suggested procedure to determine the exact location of an oil leak:
Since the rear main seal is in a position that you won’t be able to slide under your car and view it directly you need to go through a process of elimination. If you seem to be losing oil but you don’t have a noticeable drip when the car is parked you may be in the early stages of a leak. Start the vehicle up and let it idle for 15 minutes and see if that helps you identify a leak, or at least begins to show some oil leaking in the engine.
Once you’ve determined you’ve got a dripping leak, you’ll want to start from the bottom and work your way up. If you see oil dripping on the back of your oil pan or on the front of your transmission bell housing it’s possible you have a rear main seal leak.