Sorry - slightly long question:

I have sold my Mini Cooper S 07 plate 134k miles privately to a cash buyer.
Following his test drive, I noticed an engine warning light come on. I notified the interested buyer and took the car to an independent Mini specialist. They could find no fault at time of testing and reset the warning light - suggested that they could have another look if the light came on again. I notified the buyer and when he came to buy the car, I gave him the garage report which set all this out in writing. I answered all other questions about the car honestly and withheld nothing.
He bought the car (advertised at £3030) for £2500 because he was "concerned about the high mileage". Two days later he called to inform me that the warning light had come on and he was going to take it in for investigation. Yesterday he called to say that the unspecified garage he had taken it to have told him the turbo is failing and will need to be replaced - reconditioned at £1000 or new at £2000. He asked me to take the car back which I refused to consider. I believe I am under no obligation to do anything but if I was to offer some contribution out of sympathy, would I be effectively admitting any liability?

Thanks in advance for any advice, HJ.