Checking the oil level on the tcase is fairly easy. There are two plugs on the back side. The upper one is the fill plug. Clean any dirt, mud or debris out of the hex recess before trying to remove the plug. If you don't, it's easy to strip the allen head of the plug. Also a good idea to wipe any dirt off that might be around the plug. Oil level should be to the bottom of the fill hole. My 00 has a MML so I raise the back of the Jeep a couple of inches prior to checking/filling.
As far as the leak goes, do you have any idea, from the front, rear, slip yoke, between tcase and tranny? Is the vent hose attached?