I say change the fluid... if at the very least to drain out any metal shavings and to see whats inside. Drop the pan of course. I think its too late to use a thinner fluid if its internally out of spec. I cant see the gear oil, silicone, and razor blade costing more then $20 and an hour of your time. I say drain the transfer case too.

88 Montero, StarQuest turbo, Kormex 5speed +tuff-pan w/phoenix f. stage2 clutch, 4in lift+33' tires, 4.875 lsd, short-throw shifter, Aisin hubs, SR big brakes, gen2 uca's, elantra alt, and so much more... 16g turbo w/hardpipes + 4.90 locking disk-brake axle soon (maybe lsd or aussie front??)