S320/W140,rear end/pinion seal small leak.
 

I noticed that the rear end is covered in grease,underneath, and the small leak comes from what it seems to be the pinion seal in front of the rear end.It is small,no drips on the ground,however,I dont know if I should bother doing something about it,or just ad some 80w90 in the rear end thru the side fill hole.Its hard to tell if its low,was never opened before.Vehicle is a 1999 S320.