Selling a car - Do I have to declare an engine repair?

One month ago I took my BMW series 3 (petrol) for a routine service and MOT.
They called me to say there were "issues" with the car. It transpires two pieces of metal fell into the engine when they removed the spark plugs. As they were unaware this had happened, they started up on re-assembling causing damage to the head and piston. They advised previous work had been carried out on the injectors and the pieces of debris was from this.

I have no cause to disbelieve them and they offered to do the repairs "as a gesture of goodwill" with me paying for the parts. It was, in their words "nobody's fault". The cost to me on top of the original bill for the MOT and service was £720. I paid up and the car now appears to be fine. Did I do the right thing? o I take it on the chin? Also, if I were to sell at a later date, would I be obliged to declare the repair?

Asked on 1 June 2016 by DT

Answered by Honest John
They took a lot more of it on the chin than you did. I suspect that previously a spark plug had been cross-threaded and the thread had been replaced with a Helicoil, bits of which fell into the engine when the spark plug was replaced. You are not obliged to declare the repair unless a purchaser specifically asks, but if he asks, "has the engine ever needed any work?" you are contractually bound to tell him.
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