The mold is the scary part to me, everything else you mentioned should clean up pretty well. Make him a very low offer, let him think about it while you go look at more boats, he might accept or after looking at more boats you might think it's worth more and raise your offer. The worst he can say is no if you make him a low offer. It is a buyers market right now so take your time, when the right boat comes along you will know it.
Just my $.02