For your transfer case oil change, which takes about 1.6 quarts, your oil options are insanely priced Toyota 75W at $80/quart, Ravenol 75W at $20/quart, or, my recommendation; HPL 75W at $16/quart.
It’s not listed here, but if you call them, they’ve got it.
https://www.advlubrication.com/collections/automotive-lubricants/products/differential-life
Don’t forget the BITOG15 discount code for 15% off.
The transfer case drain plug is a pain, you’ll have to remove a small protective plate. It’s a square drive NPT, so it seals on the threads. I used a couple wraps of blue Teflon tape. I’ve got pipe plug sockets, but I think you can use a 3/8” extension.
The transmission can be flushed using the cooler line. Pin the thermostat open, disconnect the return line from the cooler, idle, refill, repeat until clear. You’ll need a way to refill from the side of the transmission. Total PITA.
I have a pressurized bottle, like this, that I fill with WS ATF (I used AMSOIL, next fill will be HPL green).
https://www.ecstuning.com/b-assembl...ransfer-pump-with-dsg-filling-adaptor/1735kt/
Probably worth doing a pan drop and filter change, too.
Differentials are easy. 75W90. About 7 quarts needed for front and rear.