Here is the deal with that...
The factory clutchs suck, pure and simple. But you can recork them yourself and make them twice as good. If you do a good job recorking them, they will stand up to an airsal kit with a 31/22 sprocket ratio with no problems. (with 150 lb rider)
However I did find that 31/20 gearing was too much. It detroyed the clutch in a month.
The thing that goes out on a Tomos after that is the bearing that holds the drive sprocket. And since the tranny fluid seal in on the inside of this bearing... it also goes out at the same time. So It'll start oiling your chain for you, and eventually that bearing will start screaming like a banshee!
mine didn't get bad till about 6,000 kilometers.