Re: impella
You cannot always tell the condition of the impeller by simply looking at it. Besides, when you go through the trouble of dropping the lower unit, why not just replace it. If the motor is new to you, replace the impeller since you have no idea when it was done last. Very cheap insurance. Impeller replacement can be as often as yearly if you run in trashy water. Every other year is a good average, and then there are engines that are decades old that have never had one replaced. There is no magic number. Pick your comfort level accordingly.