First look on the paypal website under disputes or claims, maybe give them a ring for their advice. then email ebay trust and safety to lodge it in their system. they will just advise you to contact the seller, but at least they then have arecord.
Paypal is an ebay company, but they work independently, so don't share info. (they may on more expensive items) but your contrct is with paypal (who you paid) so they will sort it if the seller is awkward.
make sure you have proof of postage and maybe take pics of condition and have a witness to the packing and then send back. paypal will refund you the money if you do not get it back from the seller. though this can take 28days.
they then chase the seller, so you will be covered.
it is possible the seller can raise an appeal on damaged returned goods, hence the pics and witness, but the chances are very slim as Paypal are not helpful to the seller.
hope that helps.
good luck