legaly, under new york state law, any private party vehical sale is AUTOMATICLY an “as-is” sale
it was also his responsibility to fully check the sled out before taking it home, and the fact that he took it in NON RUNNING condition just makes your case stronger
also, the damage he complains about is obviously in a hard to access place … its not like theres a piece of the cylinder head missing … he has no right to assume that you knew about it
and i think that because he picked it up here, he would have to take you to a buffalo small claims court (could be wrong, check on this) so it could easily wind up being a pain in the ass for him to take you to court