I have had chain drive, yamaha 400 special, 4 shaft drive, honda shadow, 1986 yamaha venture royale, 1989 yamaha venture royale, and 1991 yamaha venture royale. I also have two spyders, 2015 RT Limited with roughly 50,000 miles on it, and a 2020 RT Limited that I put a little over 5,000 miles on after the purchase in August of last year.
The belt on the 2015 has a groove in it from a small stone that got caught in the rear pully, that happend befor 10,000 miles on it. The dealer looked at it for the 9,200 mile service and told me that the belt MUST be changed, I chose not to, the groove was in the ribs only and not in the solid part of the belt.
As stated that belt now is at roughly 50,000 miles, at least 20,000 miles of those are pulling a camper trailer, bike fully loaded and two up. The belt has little if any visable ware on it but still hase the grove in the rib.
The ONLY complaint I have about belt drive is the vibration that shows up every now and then at some speeds.
The shaft drives on two of the Yamaha ventures had a crush washer go bad that is on the engine side of the shaft connection, and they leaked oil from there. I had both crush washers replaced and they didnt go bad a second time. One venture had over 100,006 miles on it when a car hit us and totaled it, the others both had about 50,000 miles on them.