My "differential leak" was actually coming from the speed sensor? O ring, located on the side and forward of the differential. With the car moving the few drops of fluid travel back towards the rear. Very easy to repair. Of course my car is a 300E and it may be different but, the point is, check the leak very carefully. You may save $$$$, it cost me less than a dollar , I tkink.

J.H.
86 300E