I had the first 2004 Yamaha Rhino 660 they my dealer received.
In almost 20 years, never needed a belt. I had 27 inch Swamp Witches. And, my father was going up a levee with wet, exposed tree roots. He was in 2WD and the left driver's rear tire momentarily slipped and caught traction again.
The score axle broke. I just replaced it with an OEM axle. I wasn't aware of any aftermarket ones, at that time. Never broke another.
I don't know who makes aftermarket ones, but I'll ask around.