Denny is probably right on the dampner being loose. I have heard of the key giving up on others that claimed they had it tight though. I've always worried that mine was going to give me problems at some point in time. My worry came after I was told that, after I had built the engine, I should have had a double keyway done and it would prevent problems that single would have on blown engines. Three of the serious engine builders I know do this to their cranks. I always like to get the information before I install and complete the engine . Repairing it depends on the keyway slot damage. If it is useable, I'd do the second keyway IMHO.