Hey Tod-
I understand you want him to be happy & feel you were honest; but maybe the buyer is not being honest with himself? A brake dragging some after sitting for 2 years is not unrealistic.
Honestly if I were the buyer, I would not call & question someones character (over a drag car that has been sitting 2 yrs) even if I had to replace the calipers/go through the brakes.
I think you are good guy. That was a "As is" deal.