One would hope it's not leaking from the case joint!!! Of course, that's always possible. It's very common to leak from the control shaft where shift inputs enter the case.
If your tranny is leaking from the finned adjusting nut, there are instructions elsewhere that describe how to replace the seal or o-ring. If it is the o-ring, one method that I don't think anybody has mentioned is to smear Hylomar on the threads. When I rebuilt my NG3, I ordered some new o-rings and got the wrong size
. My o-rings were probably just find as I hadn't had any leaks there but I figured the Hylomar would make double dog sure it wouldn't leak from the threads. Before loosening the finned nut, mark its position relative to the case and count the number of turns to take it off so you can get it back to the same orientation. Do one side at a time. Actually, I think snugging the finned nut will be all you really need to know but it's best to mark and count the turns.
