Sold as seen.

It is upto the buyer to get it HPI checked against this sort of thing, and it is also upto the buyer to ask for an inspection such as the AA/ RAC etc etc

I know where you are coming from Lee, its a shit situation, but at the end of the day, you sold it in good faith detailing everything you knew about it. There is nothing more you could of done short of stripping it to component level and checking yourself.