Its a hard pill to swallow but i would just let it go. He won it fair and square. He will also know your name and address now as it comes through with an ebay invoice...I travelled 200 miles and knocked at the blokes door when i got messed around...

Alternatively email him, say you dropped it when removing it, you've tested it and it seems to work ok but cuts in and out intermitently and ask him if he still wants it. I know what the answer will be....