We had a water
pump failure at 2am a couple of years ago. After we sailed to safety
and I found out the key in the impeller had failed. Turns out it was plain steel
and had corroded away. We had gone to full power to get out of our situation and the key finally gave up the ghost under high load. I whipped out the angle grinder and made a new one out of a 1/2 stainless bolt and it has been there ever since. Partly because the new key was a tight fit and I have not wanted to ruin a good impeller trying to get it back out.
A month or so ago I stopped at the go-to water
pump shop in Oakland/Alameda to get a proper key. It turns out they don't have stainless keys either and they did not know or realize that all their spare keys were plain steel
So as a heads up, check your key the next time you can.