If the impeller is failing and there is water getting to the pump than I agree that the culprit is the cam. I recently found that the cam on our pump was chipped at the top end and that was shredding the impellers. As already said, it is easy to replace the cam by removing one screw. In an emergency the cam could possibly be turned end for end thus moving a sharp chipped end away from the leading edge of the rotating impeller. Alternatively a chipped cam end could possibly be smoothed with a file as a temporary repair. Richard.