You definitely found the problem. If the same guy who rebuilt the engine installed that water pump it kinda lines up with the rest of the story right. I'm very dyslexic so I lay the service manuals right next to where I'm assembling something or in a Outboard engine's case I use a computer outputting to a 24in monitor with Boats.net exploded diagrams pulled up. I match the part numbers before placing any part in place. No Guessing At All. The cost to replace a Powerhead to the possible monies made is too high a risk for me to even work anymore. Newer Boat owners do not have the common courtesies to know repairs do not happen fast, are not cheap, and are not warrantied against stupidity. Especially if they want perfection. My older customers knew, Rojo is not fast, he is not cheap, and he will close his shop if he thinks the Crappie are biting. They would pick up their boats and never return because I didn't fix something right. Today's Outboard Mechanics are parts changers not troublshooters.