I've yet to hear of a full sprocket, gear, and tensioner not resolving the issure, though I doubt the tensioner is THE problem. The key linking the crank to the sprocket is the failure point, IMHO. CHEAP **** keys get screwed under pressures. The sprocket gets to wobbling and the chain is damaged. Replacing only the gear and key (still likely to be crap steal) and the new gear is beat up by an imperfect chain. Sure we'd much prefer a key replacement than a crank but why not put it together right the first time.