Main question is about the Transfer Case:
I put in Castrol Syntec SAE 75-90 full synthetic gear oil...(similar found here black bottle, red banner at the top ...and I've had a case of it for years but finally used it in my front/rear diffs and transfer case.
fwiw the (manual) transmission got redline MT-90 and I have a quart of it left over.

The point here is if that oil is okay for the 1988 transfer case?
It only says gl-5 on the back where it states :..."performance that far surpass conventional API GL-5 and MT-1 gear oil."

bottle states :
Fully synthetic, API GL-5 and MT-1, SAE 75W-90 formula.
SAE J2360 (MIL-L-210SE) approved.
meets and exceeds conventional and synthetic gl-5 gear oils.
Friction modified for use in both convential and synthetic axles.

However, I've recently read that maybe *some* transfer cases will have syncros and I don't know if mine does or doesn't...or if the transfer case has brass in it and if so, if this oil is okay or not for brass?

Before I spend any more money I'd like to know these things.
please and thank you.