My nephews 24 ft htm has a 565 gen v 10-1 motor with edelbrock aluminum victor heads , roller cam, dominator , lightning exhausts, and has been running fine for years. All of a sudden at 5800 rpm it starts to miss a little so he brings it back home and we remove the sparkplugs. # 3 cylinder spit out quite a bit of water when the plug was removed. Turned engine over and more water came out of that hole. Did a leakdown and that hole is 18% leakdown. 1 , 5, and 7 are at 4 % leakdown. Removed intake and gasket is solid stuck with NO evidence or leaking around port. No water in oil. Removed head and it has felpro 1075 mls gaskets. No sign of any leakage around combustion chamber. There are signs of some water spots in cylinder from most likely a getting worse situation to the point of misfire. Cant find any sign of a crack in the cylinder, head . A close inspection of the lightning headers , which are 12 years old, shows no signs of water going thru that header tube. What to do next?