I have been having an overheating issue on high rms only. I replaced impeller,thermostat,shift shaft bushing(gear oil leak as well). I remember taking the impeller apart after original install and found small black I think plastic pieces in impeller housing. The impeller did not look degraded in any way.Could this be the exhaust flapper and if it could be can it be removed or checked anyway with the boat in the water. Dont want to sink if i take the exhaust bellow off!!! When I check the oil it is high before running and fine after I shut it off? It was recently changed but I cant tell if there is water in there it is not milky. Used quicksilver oil so not sure if it will mix when water is on oil pan.