For 2016 Grizzly and Kodiak Final Drives (rear differential like box), Yamaha specs Mobilfluid 424 which is hard to find. From another thread I learned that lately Yamaha dealers have been recommending, "Yamalube Friction Modified Shaft Drive Gear Oil". It is available for about $10 per quart.

Here is more info about it:
"Specially formulated especially for quiet operation and proper performance of the sealed wet brake final drives and standard differentials of all Yamaha products. It contains a superior anti-wear and anti-scoring performance additive and a dispersant inhibitor system to help maintain seal pliability to prevent leaks."

I wonder why this isn’t spec’d for the front differential. For the front diff we are supposed to use "SAE 80 API GL-4 Hypoid gear oil" which is readily available and costs about the same.