I just bought a used boat from a private party last fall. The guy told me he changed his impeller out every two years for maintanance because the lake he primarily ran in had a sandy bottom. The indicater flows a nice powerfull stream. In fact, I was commented by two different people last year that it looked like a healthy flow. I am not sure if he put in a new one one year ago, two years ago, or more.(Sometimes you can only trust people as far as you can throw them). My questions are: Should I bother checking it out if it has a nice healthy telltale already? How often should i relplace the impeller? Do you just replace the impeller or do I spend the sixty bucks and buy the kit with the whole housing, impeller, cover, and gaskets?