Originally posted by loubapache
...So make sure the source of leak is exact.
GREAT advice. The M104 is not known for leaking main seals, unless someone overfills the crankcase. (As one of my local dealers does...)
It can be tough to figure out where it is leaking from, but get your mechanic to try REALLY hard. No sense replacing a main seal only to find out later it was the head gasket.
BTW, in most MB's I've seen with a leaking rear main seal, the front seal is leaking too from the cavatation of the oil in the crank-case.
Also, if the crankcase was consistently overfilled, it will dramatically shorten that catalytic converter's life. These are the reasons I do my own oil changes...