,a fellow RSC memeber posted here a while back that he contacted Yamaha technical staff at jheadquarters and asked if it was in fact ok to run the lube with GL hi pressure additives and they said it was fine,not an issue at all so your good to go.
I an running Mobil 1 80w-90 LS syn lube in the transfewrr box on my 06 silverado & so far so good with 5k+ miles on that lube.
If your still worried you could try Royal Purple's new Max Gear 80w-90 lube.
RP's max gear lube has the latest generation of GL5 hi pressure additives that aren't as harsh/corrossive as the older older generation GL5 additives couls be in some situations like for ex the yellow metals used for syncros in older generation manual trans like GM's Muncie 4spd used.
As far as i can tell the transfer case on our R*'s doesn't have any yellow metal type bushings etc in it so if that's the case even the older generation GL5 lube with the more corrossive hi pressure additives would not be an issue.
If you must have GL4 only lube you can order Staylube's GL4 conventional Hypoid 80w-90 gear lube from your local NAPA.
Heat bike/transfer box & oil up ,drain the trasfer case,then refill with approx .45-.50qt (1/2 qt lube)and your good to go.