We recently had a raw water pump impeller failure causing the engine (M25 Universal) to overheat. As it turned out it was the rubber part of the impeller that got somehow disconnected from its core (a medal cylinder). In other words, the connection between the two parts, which should have been solid, allowed for slippage between the two. (Not sure how the manufacturer secured the link between two parts to form one unit, glued?) The rubber part looked still like new so this must have been a mechanical failure and/or designer flaw. Not sure if the impeller was an aftermarket unit bought online. After inquiring with West Marine it appears that recently there have been similar reports of such a failure. Caveat emptor!