Yanmar YSE8 seized

[Mobcat]

Hi all new to the scene I have bought my self a new yacht with a seized Yanmar yse8, I don’t know how it’s seized but I suspect over heating but maybe not ? I suspect over heating because the water pump">raw water pump was seized but that may of occurred after the seizure, anyway I have tried all the usual to no avail breaker bar on crankshaft trying to rattle it with the starter motor with injector out and no movemeto of the piston ….. bottom end seems fine no water in oil etc ….. so I removed the head and what I discovered was a corroded mess in the cylinder head actually seems ok, but I still can’t get her to turn once I have removed all the gunk and sprayed WD40 in it over night repeatedly….. what’s next crew any ideas …. As usual cash is tight bla bla bla otherwise I would have a super yacht with a crew and wouldn’t be here
Thanks in advance