I just got back from having the dealer do an oil change for me. On their list of things that "ought to be done" is to troubleshoot a transfer case leak. They will charge $185 to diagnose it, then I would find out what it would cost to fix it.
I asked if they top off the transfer case lube given that there is a leak. The service writer dude told me that the transfer case is sealed and that there is no way to add fluid! I was skeptical but didn't argue with him.
This video shows that there is both a drain plug and a fill plug, just as I would suspect. The service writer is clearly clueless on this.The guy in the video uses synthetic valvoline 75-90 limited slip fluid. He finds that just a little over a quart is required.
He emphasizes to take care when tightening the plugs since they are going into an aluminum casting and stripping them out would be a disaster.
Tom's Tacoma pages / tom@mmto.org