Oil leaks can be tricky... Make sure it's not coming from the top end, not sure what engine you have, or oil pan. Those are easy to fix. Sometimes you can change the rear main with the engine still in place by slightly lowering the crank and tapping it out then use a chinese finger to pull a new seal in the top. I picked up a rear seal removal kit a few years back and did that with a V8. Leak is gone.
Here's a link to the concept... I got mine at a local NAPA
I am curious as to what motor you have in your YJ that would create the need to loosen the crank or pull the motor out (as inferenced by your statment about leaving it in). If you have the 4.0L or pretty much any other motor, then you been doing a lot of extra work.
i had those symptoms when my rear seal went out. there was just a wet trail of oil down the pan and a small drop by the plug. i got mine fixed under warranty so i never even looked around under there. i just took it in.
If it looks like it's dripping down the bolt..... Check and make sure the bolt is snug ( all the bolts holding the oil pan ).... Not too tight, just like valve cover gaskets, get um to tight and it compresses the gasket to much and it will leak.... Like others have said, check the top end of the engine... Reach back there and feel for grease......