In a similar story, Kat and I sold her Micra '06 on 32,000 miles. I passed its MOT but we was leaking oil but no idea where it was going! Arnold Shark wanted stupid money to replace engine so sold on eBay as an auction.
Ended up with £2000 from a garage down south which was more than expected but it was a mechanic so he obviously though he could fix it easy and resell it.
He was wrong! He got a guy to collect it and drive it down south, we gave him oil as it needed topped up every 150 miles. It supposedly broker down and was smoking at exhaust (never did with us) gave the threats of legal action as not as described and said it was obviously a dodgy garage that passed its mot (he didn't know it was AC) he demanded £250 to cover his loss too.
I emailed him, copied my description on eBay, explained who did the MOT which was where it was also regularly serviced and told him he had no chance of any money. If he wanted to go to court, he was welcome to but he had I chance.
Never heard from him again!
(used the money to buy the mk2 110
)