I replaced my 46rh in my 94 dak with one from a 92. In 30 miles or so, a quart or 2 of fluid is missing. I noticed the transfer case is leaking fluid from the rear output shaft. Is it possible that fluid is leaking from the transmission into the tcase and then out the rear output shaft? It seems to only leak when the truck is driving. running the engine in park after driving, a drop or 2 will come out and it will no longer leak.

Trans has 120k, but is not making any weird noises or slipping and a 5 speed is not in the plans until late spring, so i need the trans to last at least 3-5k miles.

The tcase is from the 94 with 180k miles. the fluid was black and smelled like motor oil when i drained it. Is motor oil even an approved fluid for the tcase?

 

No motor oil cannot be used in the transmission. Use ATF 3+ or higher
The loss of oil can be due to the torque converter needing fluid.