Before you tear into it, get yourself a manual, or check out the Online Chevy Manuals Project
http://chevy.tocmp.com/. Good info there on repairing anything on the truck. That diff is plenty strong, it also boasts a larger ring gear and axles than the later units. There is a place, Toms Rearends, that makes a conversion to 30 spline axles, using later 12 bolt side gears, if you do end up needing to upgrade. I have considered doing this myself, but am going to do some more research first. Gaskets are still being made for this diff, Fel-Pro #RDS4304.
