I wonder if this isn't a scam, appears like old mate deliberately held out on you K.
He gets his money reimbursed, and gets to keep the part too. Its only his good will to return said part to you. And really, how will ebay force him to return it. He just kills that account, and starts another.
Ridiculous in this day, and age, that ebay favours the buyer. You'd think they would investigate, and then deliver a verdict. One of many things I dislike, about dealing on ebay.
Hope you get your part back bigk.
Cheers, Mark.