Both (!!) times I have returned mine for a replacement case, I have done this using the Live Chat service, followed by emailing them a picture of my crack (ooh err!) - something they insist on.
The first time I sent mine in, they sent me the same one back with a new case.
The second time, they sent me a replacement.
The replacement LOOKS brand new - this is possible, because mine is a 64GB white one and these were scarce outside HP (20 sold by John Lewis and no evidence of any others in the UK.
Hopefully this will last longer....
Anyone know how to transfer the ADP from the old to the new device? I presime more Live Chat is required....