If you haven't sent that back yet, I'm telling you it would be probably +/- $10 the cost to send it back compared to the cost to buy a complete, new case back. Do NOT send that watch back to China. Reiterate to Sead that you want a new case back, even if you have to pay a little bit.
I wish you could take a REALLY clear picture. If it's something easily fixed (not too deep), i'd refinish the back for you myself.
Any H or N factory 111 caseback will be a direct replacement. It's a 1 minute job that requires nothing more than a ball of wadded up tape. Do not send the watch back. Wear it, and source another case back. Post a WTB in M2M, someone has 10 of them laying in their desk drawer.