I have a 1974 Ford F250 RWD that I use very rarely. I take it around the block once a month to make sure it still works.
A while ago I noticed that the rear differential was leaking from (what appeared to be) the cover gasket. I replaced the gasket and it's still leaking. It now seems that the differential is leaking up where the driveshaft enters the differential.
What is likely to be the problem here? I couldn't find any relevant info in my repair manual.