In Ireland every private sale is sold as seen,the only way he can have comeback is if
You refused to let him bring a motor mechanic.
You fix,sell or are otherwise involved in the car trade.
You covered up a dangerous defect with the car and knowingly sold it as such. This bit is the hardest,he will have to prove you did it which is harder than it sounds as it can be one of the few instances where ignorance can be a defense. Your not a mechanic,how would you know?
Give a local solicitor a ring and he can tell you down the phone,but I'm pretty sure caveat emptor is the same as in the south of Ireland,plus it will give you more confidence when dealing with him.