There is nothing you can do through eBay. They have no further interest once their own 30 day money back guarantee has expired. I'm afraid that warranties given by eBay sellers often prove to be worthless.
The best thing to do is try your payment provider, e.g. credit or debit card issuer, is this is how you paid. They may be able to help, especially if you paid by credit card.
Otherwise, if this was a UK business seller you should have some statutory consumer protection rights, but having rights and being able to enforce them against distant, uncooperative eBay sellers are not always the same thing - especially if the seller has left or been removed from eBay. Take legal advice first, or consult Citizens Advice.
Good luck, but I'm afraid that these are the risks of buying from unknown sellers on eBay. What sort of wooden or metal replacement part does it need? It might be that you could find someone locally to make one.
