Have you got an invoice etc and how is it worded?
You inspected it and paid, so to use your own words you were happy
Did you get any other independent inspection AA RAC ?
Also he could claim that you did the damage by driving it with a water leak etc, which happened after he sold it to you and he's only prepared to pay for the initial water leak as it was your continued driving that caused further damage
Barristers, Solicitors, Accountants allegedly
First meeting your 100% in the right
Second well things could be more difficult
Third it'll be 50/50
Fourth here's my bill and I'd do a deal with them if I was you