The rear input shaft oil seal on the auto box is in the transfer case. How do you know it is leaking? Or do you mean the rear output oil seal inside the hand brake drum?
Remove prop shaft and undo flange nut with hand brake on or use special tooling. Back off adjuster. Remove handbrake drum. Remove and clean handbrake shoes. Remove flange. (Note that oil seal it is inset into housing not flush fitted, measure intrusion.) Check flange surface for grooving, if it is badly worn, when oil seal is fitted, fit it a little further into housing. I made a tool for this purpose, oil seal needs to be fitted dead square in housing. Grease oil seal and fit, grease flange and refit. Refit shoes and drum adjust handbrake and apply to torque flange nut. Or hold with special tooling. Replace propshaft.