The first thing I would check would be the valve cover, you really need to clean the motor before finding it though and remember oil always leaks down not up.
As for the tranny leaking, usually they don't, unless you overfilled it somehow like pouring the lube in from the removed shifter or having it pointing nose downhill too much, usually it's the transfer case rear seal that leaks. As for doing the pinion seal, personally I would take it to a drive shop, you do it wrong and it's some big bucks to fix it. There is also the issue of torquing the pinion back on, 250ft lbs comes to mind and thats one heck of a big pry bar on the torque wrench. The other place it can leak is the O rings in the oil filter mounting boss, jeep sells a kit for that.
For driveline stuff I go to performance driveline down the street from Blue Mountain Ski area up here in the pocono's.