I concur. Only thing in that area with gear oil is your transfer case. Most common places for leaks are the front and rear driveshaft seals which is a relatively easy fix as the driveshafts are easy to remove and replace. The tricky part is putting the new seal in properly without damaging it. Of course it could also be the main seal between the xcase and the transmission.The transfer case has gear oil. Check the oil level.