My experience was this on my 95 XJ... I had read all the posts on this subject, and checked everything I could find Could find nothing. But I was still getting a slow drip...Coming over the Sierras on way to Baja , we pulled into a rest area and had oil smoke billowing out from under hood.
I figured we'd blown the main seal completely.....We found a mechanic through a friend just north of San Diego willing to put it up and look at it. He said take it to a car wash and clean it up then bring it by.
We did....He spent about a half hour looking it over. He decided to check all valve cover bolts. He found four loose ones in the back. One by more than two turns !! I had looked back there, but I couldn't find any oil.....
Well that seems to have solved my problem. We also replaced the PCV valve. Even though it seemed to have been the problem, I was still seeing small amounts of oil coming down....But SLOWLY over the next 1000 miles The,. It stopped. I am guessing it just took a while for the oil to boil down and off.??
Anyhow....as stated before on this forum....there is a good chance its something other than a main seal.. Good Luck

 

Extremely common to have the rear valve cover bolts loose.