I remember the thread years ago about impellers being changed yearly by some. Mine was 15 years old I think when I changed it. Signs of wear but still moved enough water to cool engine.My Tracker is 10 years old now. Finally did a "tune-up" on the 115 Merc Optimax. Replaced the fuel filter, air filter, and spark plugs.
Cost me like $75 including the special tool to remove the fuel filter cap. Oh and did the impeller also. That was another $50.
Actually the spark plugs looked fine as did the impeller-