TII has been leaking fluid in the rear for awhile. I was wondering if the diff had some kind of pressure release that could get clogged?

When checking the fluid today I noticed a small hisss of pressure release after removing the bolt. Is there a common seal that should be replaced? If it is a seal.

 

The differentail pinion seal is the likely culprit. It is the seal on the flange which the driveshaft bolts to. Be sure to check the two stub shaft seals too. You want to take care of everything at once vice draining the diff. multiple times.

Matt