You know, I really like that permatex aviation sealer, I like to put it around the rim of seals before I drive them in as it acts both as a sealer and lube. I've seen it used in assembling aircraft engines, as a sealer between the block and crankcase after a silk thread is laid down in it--yeah, odd. I've never used it as a sealer though on Transmission or Transfer case housings though. It just somehow to me seems inadequate. I just feel more comfy with stuff like FIPG, like from Toyota, or the Red or Black Permatex RTV stuff.
In restoring vintage metal case chainsaws, such as the old Roper 3.7s that have the fuel tank formed by putting the case halves together, I use Yamabond which is fuel safe, whereas RTV had dissolved in the gas, and leaked. I have not found this necessary to use in transmission or transfer case assembly though, and use the Black or Red RTV without any issues. I've built up a ton of transmissions in the last decade or so, and have had no leaks. Mean Max has also built up a ton as well, and never said he had a problem with Aviation Sealer; I just can't seem to make myself trust it though. Sorry Max, wherever you may now be.
The Ultra black is good stuff, just wear rubber gloves when you put it on as it seems to get everywhere and is a challenge getting it off your fingers, out from under fingernails, and ear holes when you make the mistake of itching your ear hole when you have it on your fingers. Oh, sorry, "external auditory canal," of course.