However, if the seller does exactly the same with you as he did with me (i.e.: nothing) then you'll win by default and get all monies back.
Also, I did have to call Paypal myself to get the refund after the 10th day of the claim going in, they then had to contact Paypal in Germany to decide if my claim was valid enough to warrant a refund. If you've used the resolution centre for all correspondence with no replies from the seller you'll be fine.
Edit: And yes, I still have both bumpers here and haven't had any contact from the seller requesting them back. I'll more than likely Ebay the M3 style one but I have no idea what to do with the first one that is too big?