This is the only vehicle I've ever owned that didn't give a gear oil rating for the final drive. It says "Hypoid", but no GL-4 or GL-5.....I see what everyone else is using, but I've just never seen this.
All the other bikes with final drives, and autos I've owned specified GL-4 or GL-5. I guess it's more important in a tranny, where most GL-5s don't work very well with synchronizers, and "supposedly" (I think it's BS) eat away at the yellow metals such as bronze and copper in the trans. I don't believe the last part, but I've experienced first hand about putting GL-5 in my transmissions. Cold weather shifting was so bad, I had to go from 1st to third, until it got hot. Had nothing to do with the weight, just the ep additives.