The front diff drain plug:
I believe that Jeep just sells this as a unit.
(Edit: Mopar part number for just the o-ring is 5066055AA.)
If the threads look good, just replace the o-ring if needed.





You need a 70 or 75 durometer Viton, polyacrylate (ACM) or nitrile (NBR, Buna-N) rubber o-ring. It should be a standard AS568-114 (5/8 x 3/32) or metric 2.5 x 15.5mm.