In additon to above also verify if the oily residue your seeing isn't cosmoline. In some areas of the undercarriage it does look more like oil than the waxy substance you see in the engine bay.

Fastest way to determine for sure if the diff is leaking is to have the undercarrige steam cleaned and check for oil after a couple hundred miles of driving. If the oil reappears then you'll know it's leaking.

Good luck.

__________________
Afshin

Current:
02 C32 AMG

Previous:
92 500E
84 190E 2.3 5 Spd