Have Dana 80 rear, broke axle (at hub!) and had it replaced at shop. Since then diff fluid has apparently been leaking out of the vent tube that runs from the top of left housing (connected to a hollow bolt that secures the brake line splitter to the axle) and runs vertically about 2 feet, secured above the spare tire. The fluid is easy to trace as it lights up with UV light! It does not leak on short trips, only after 1+ hour. Fluid level check was just slightly below fill hole. My only guess is it overheats and foams or "boils" up, have not checked the housing temp but will do this next. Do not know what fluid +- additive they used. Any suggestions on diagnosis or fix?

 

Drain it and refill with correct fluid...sounds like it is overheating and expanding quite a bit.

Just my .02

 

Did you solve this yet?