Berger...just a quick question...is the impeller that is eating itself up, on the engine that you are having heating issues with? If so, maybe you do have some sort of blockage in the raw water circuit...?
I usually get at least 300 hours on an impeller. BTW, to leave an impeller in the pump, while the boat is in storage for several months, is hard on the vains of the impeller. I remove my impellers, when I store the boat for the summer months in Lauderdale.