I have a 1991 325i with a manual transmission. I've been noticing whenever i leave somewhere, i'm also leaving a little puddle of oil. My dad went under the car to 'have a look' (he isnt *real* knowledgeable) and he says its the rear main seal thats leaking. How much does this cost to fix? Is there any way you can tell for sure thats the problem? He says the leak is between the transmission and the engine.