SAE 80 API "GL-4" hypoid gear oil says Yamaha. Replace every 16,000 miles or every 2 years. I use a synthetic 75W90 which meets GL-4 and GL-5 requirements. Fill to the top of fill opening.... About 198cc- from memory.
Any gear lube designed for a 2 stroke/wet clutch gear box!!! I use Torco MTF 80 wt. which meets Yamahas 10/30 trans specification!!! Been using it for 10 years on many Banshees with no problem!!!!
if its a first gen vmax any good 10w-40 motorcycle oil. i use mobil 1 4t motorcycle oil, some will say synthetics shorten the life of the clutch, i never had a problem, just stay away from automotive...
in my 2005 Yamaha xvs 1100 i use penrite 5w 40 because it helps with the gear change .is a lot smoother because clutch plates don't seem to stick as much.give it a go.