I noticed my rear end has some seepage (no marks on the ground), just where it gets all black goupy around the fill plug and on both sides of the differential case where the larger pipe connects to the smaller one which houses the axels. The area where they connect and there is a stamped rivet combining them. They both seem to be seeping from the same area on both sides.

My a4 car doesnt have this, but my 96 m6 one does and so did a 95 m6 one I looked at a long time ago. Is this just a manual thing where it puts more wear on the rear end?