Here is my rig - owned for 1.5 years - '01 limited 4x4 - 115k - awesome truck minus the overheating off-roading, fixing both axle seals and some rust from the NE. Cheers!
As far as the rear axle oil seal goes, you can tell from the oil on the inner tire as well as inside the rim. If you are lucky it is just the seal, not the entire axle. Cheers!