I just changed the gear oil in my differentials this weeked. The drain bolt has a magnet in the middle and I was surprised to see so much 'gunk' stuck to it. Now I really am glad I changed it because at one point I was questioning whether it was worth it.
I used 75w-90 Amsoil gear oil and used two new crush washers and it was pretty easy (expected).
BTW gear oil F'N STINKS to holy hell
. I felt like taking a shower when I was done.
Lastly I still have to do the transfer case next weekend.