My differential is leaking at the fill plug. 1995 f-350 2wd SRW 4.10. Badly enough that anything I tow comes home stinky and slimy. I checked the plug, crazy tight. I removed and cleared the vent tube and the fitting where it attaches, no change. Also noticed that the diff was pretty warm after a 8 to 10 mile run. Then again, I've never seen the need to jump under my truck and see how warm it was before either . Not sure what to think. Anybody had a similar leak before?

 

if it was crazy tight it could have cracked the housing. get a new plug and try it.
as far as temps, my '97 has a temp gauge in it. 10 miles doesn't even move the needle off of the bottom (100 F) running empty about 120F, empty 35' gooseneck (6,000 lbs) 130F, truck trailer and hay (see signature) 230 was the hottest I have seen on a long hard pull, normally 190 to 200F with that load (27,000 lbs)

 

Mine was too, wrap the plug threads with white teflon tape, then reinstall,no leaks for years