I am going to change the oil in the NP205 transfer case and I don't want to run 80-90w oil in it if the seals fail between the transfer case and the automatic transmission in the future.
It has ATF in it right now as it was delivered from the factory in -86. So, I have been studying oil on the Internet and in brochures and came to the insight to use GL-4 tractor transmission and hydraulic oil UTTO-type. It is a "mild" hypoid oil for not-so-hard working hypoid gears even though the NP205 is not a hypoid gear type like an automotive axle. Tractors have a lot of side cut gears just like the NP205 and are running long hours. This oil is also working in tractors with multi-disc transmissions (power shifts) and wet brakes.
So my thought is that in case the seals break in the future and oils are mixed the TH400 will not suffer any harm, at least this is my theory.
Feedback please! Thanks.