What should i do?

Yeah I agree with MHM and rriggs

Take his offer for 50:50, sounds reasonable, the gentlemans agreement.

Afterthat send Redhand round

What are the symptoms again? You have a couple of threads asking for advice, if you condense the main problems again in a single thread

if your thinking about keeping it, the head gasket is a job worth having done, peace of mind and all that. If your not going to keep it then don't bother. BUT if someone asks you about it when you sell it, you have to be truthful otherwise the buyer can come back at you. You can always lie, but you would have to ask accy nicely to change your user name otherwise anyone doing an internet search will find this thread, hey presto, evidence for court.

Do unto others as you would have them do to you.Just remenber what goes around comes around