We have found that the oil filler cap can get worn out and actually have oil blow back out around the seal inside the cap, I've also had a dipstick seal (where it goes into the tube) dry out from the heat and blow back up the oil tube. A bad pcv valve can cause enough pressure in the engine for the oil to find a way out. Other than that it seems like trouble shooting time and degreaser.

http://www.jeep-shop.com