mercury 150 xr2 water drops on spark plug

[arctic cat 1000]

Thanks to the help on this forum I have my 1987 mercury 150 black max running very well. The motor has very low hours. It sat for a few years and I bought it this summer. I rebuilt the carbs, Fuel pump,replaced all fuel lines, Water pump and all parts, rebuilt poppet, New thermostats,Installed temp guage and water pressure guage ,added fuel water seperator,Mixed oil and gas 40.1 and used stabil ethanol treat and flushed out the boat gas tanks. New stator,Disconnected oil injection with proper parts and removed the advance module its wires were all burnt. And bought a factory service manual, The motor runs great and idles fine turns 5600 rpm and does not overheat. The problem I had was number 6 spark plug the bottom one on port side had some water droplets on it after I ran it. So I replaced both head gaskets on both sides and exhaust chest gaskets and seals. Ran it on the hose and still getting water drops on this plug. Compression is 120 on all cylinders. The motor has never been overheated that I know of and has only seen fresh water. When I had the head off. Number 6 piston had carbon on it and is not steam cleaned the cylinder wall had no scratches and you could still see the crosshatch . Could it be the powerhead base gasket or a bottom seal on the powerhead Letting water in any Ideas.