There are a few posts here giving step by step info on how to change the pinion seal. It seems like a pretty straight forward job, but if mine should start leaking, at an average of $100 to have a shop do it, I will opt to forego the hassle. Do a search on "pinion seal". I just changed my diff fluid today myself. The rear on these trucks call for 75w_145 synthetic, with friction additive for limited slip units. The front on 4 wheel rigs take 75w-90. No gaskets on diffs, use hi temp rtv to reseal. Don't know how much the front takes, but the rear takes just over 2 quarts.