Lee I said this in PM but ill repeat here.
its his problem mate, all you need to do as the seller is say it had been dropped, which you did.
the rest of the onis (sp?) is on him to get it checked over.
Rich said it better than I did via PM but totally true
sell you my cossie with a blown headgasket. You know that, but you still choose to buy it. You take head off and find the head is warped because the car overheated which caused a headgasket failure. Would you expect me to take the cossie back because the head is warped, even though you bought it knowing there was a headgasket failure. Would you have the balls to even ask me. i would say get lost, you bought it knowing the problem and what other problems a headgasket failure brings with it.