In my article in the March 2011 issue of the Times entitled “Tech Tip: If Your Rear Axle Is Noisy”, in discussing leaks from same it was suggested that you “check the pinion seal as well as the large, round gasket where the differential meets the axle housing…”.
However, I neglected to mention that another source of leakage from this same area can be from around one of the 12 nuts fastening the differential assembly to the axle housing. Check the nuts to make sure that behind each one is a special copper sealing washer. If such a washer is missing or damaged, or if an incorrect ordinary steel lock (or flat) washer has been substituted, a leak may result.