I'm certainly no expert at transmissions, simply a shadetree mechanic that reads a lot and collects one time use tools.
About two weeks ago I repalced my drivers side Differential seal. That's the one you can see surrounding the "stub" after you get the half shaft off.
The seal was about 8.00 from the dealer. There is also an o-ring that goes around the the part that unscrews. that one I didn't replace, but probably should have. I guess I just didn't think it would go bad as there really isn't any stress on it.
Anyways, If you do decide to unscrew the part that holds the "stub" make sure to make a MARK with a Sharpie on both the differential housing and the part you're unscrewing, VERY important. Then COUNT the number of turns till it will come off. Take your time, go slow and keep checking if it has come off or not.
Once off, WRITE the number of turns down so you don't have to remember it. Be exact, for example; 4.5, or 5.25!! (mine was 5 turns.)
Do your work and then replace the the part you unscrewed VERY carefully. Get the part's threads to catch and then count the turns back and line up your marks perfectly. This is really important as the differential bearings are preloaded and you want to make sure that you keep the same load after getting in there. Also only do one side at a time. Then screw the small toothed holding plate back on and you're done.
My dealer's parts guy told me this when I bought the seal and I'm glad he did b/c I wouldn't have known. (which is why I don't do this professionally)
You'll get some fluid draining so get a bucket. Also some clean rags to make sure you don't introduce dirt into the differential. A round 3-4 in spacer fell out when I did this job and I thought I had screwed something up but I just put it back in. Can't remember if it only went in one way or not so be careful and look it over first if it does come out.