I would be extremely careful with this one and would say your first port of call is going to be to give ebay a call and see if they can advise you. This is exactly why I don't use the GSP!
I had a similar incident a while ago but I was the buyer (UK) and the seller was in the US. Once I'd raised the case, the onus was on the seller to provide me with a pre-paid shipping label to get the item back. The ebay system wouldn't actually allow this due to me being in a different country so the seller kept saying they would talk to ebay. Eventually after seven days with no shipping label the ebay system refunded me the price of the item (which I still had) and my postage!
The seller was seriously out of pocket; in my case they were a total dick about it so I didn't lose any sleep.
I would imagine the cost for the buyer to get a wheel back to you is going to be a fairly large chunk of the value of the item in which case the best thing would be if you can persuade them to keep it.
The GSP is a bit shit to be honest and doesn't accommodate international returns at all well.
At least if you can get ebay to shoulder some of the problem they may be able to help determine the best way to proceed.
Regarding the jacket the buyers obviously a twat but best thing is to cancel the transaction (specify reason as 'requested by buyer') relist and move on. Block the buyer also. If you still have the item there's never a good outcome trying to force a sale. Even if you got them to take the item; they could just say 'not as described' or damage it themselves, claim damage and ask you to pay for the return!!