1040884
I just recently replaced mine. It is the little egr looking valve on the rear of the valve cover. The guy at Jeep called it a CCV (Crank Case Ventelator), and it only cost between 4-5 dollars. You can replace it in about 5 minutes.
Check your old one and see if there is a bunch of crud in it. It should have a little visible hole in the bottom that lets air circulate through the valve cover. Mine was pretty well covered. When it gets clogged up, the oil gets blows out as pressure builds.[addsig]