your dealer is 100% correct. The exact thing just happened to me. I stupidly tightened the back idler cable because the drums (elephant ears) were very loose but then it pulled up that back sprocket and the bearings were exposed. What happens is that idler cable stretches over time and instead of tightening it you should replace instead.
The Center Pin will wear out and bearings will if its too loose. Also the stock grease is not very good. Get really good Marine grease and redo the main pin, roller and the two pins by the chain. It will run much smoother. Wash with fresh water with good pressure to get rid of sand and debris.
It's a design fault as far as I see. I and my mates had same issue and hence we have replaced carbon pin bearing with ceramic ball bearing and works like charm. They should sell sprocket only not the entire assembly.
