I don't get it.
You bought a lemon on ebay, so I'm guessing not seen or tested it. It had major issues which you then fixed, doubling the cost of the car.
Now you are seeking an apology, compensation, a pound of flesh? Or do you plan to take 'the boys' to give him a duff.
From a purely pragmatic point of view, you are unlikely to have any successful recourse. You drove it away, so it was working. Its now also working. This is what the seller will claim im the event of a legal claim.
So really you had 3 choices on descovering the fault
Seek recourse from the seller
Fix the problem
Sell the car on with known faults at a loss and buy a new oue
If you belive that he is a trader selling pups privately to avoid comeback. Report to trading standards and to HMRC (as ypu can gaurantee he's not declaring them).
Edit. I hope yodo get a positive outcome, I just dont see it happening im afraid.
