While re-installling my drive shaft with greasable joints, I decided to check out a few other things and noticed I could move the rear tires up and down with a noticable clunk. Removed axle and sure enough the axle bearing nut was too loose. Re-adjusted per service manual procedure and all is good. Can't help but think this may be the reason for pre-mature axle seal failure on the one ton axle. Proceedure is to tighten nut to 50 ftlbs while rotating the wheel counter clockwise and then back off the nut until it is finger tight and lines up with lock slot, or back off to the next looser slot if it doesn't line up.