Do you have a place to work on it? If you do Jeeps are fun to work on. Degrease all you can, and then look. I recently used the UV dye $8 you put in your crankcase, drive it, then at night use a blacklight and shine it everywhere you can. Leaking oil will glow. In the order of easiet/cheaper to harder are the things to check and/or replace, IMO.
1. check ccv on valve cover, make sure it isnt clogged and that the hose connected to it is pulling a vacuum, if its not breathing the pressure build up will force oil past the seals
2. oil drain plug
3. check the oil filter
4. oil sending unit
5. valve cover gasket, mainly towards the rear
6. rear main seal
7. oil pan gasket
8. timing cover gasket
I literally replaced all except timing cover gasket. A few people I have talked to told me that if its a high mileage engine, the crank MAY be worn to the point where oil is going to leak past a NEW rear main seal. 199,670 mi with a very steady drip when I bought it and 300 mi later a less than quarter size mark after its parked. Thats acceptable. Good Luck and "Become one with your YJ"