I guess I never considered a warranty on a plastic box! But I've only had one ever to fail and it was my fault. It was full of ammo and I accidentally dropped it! Like the others have said, not worth the postage to send them back. It would be worthwhile if they would accept a picture.
I have a bunch of those Herters boxes. Mostly for 20 round rifle cartridges and 25 round shotshell. I have enough MYM boxes that they should send me an invitation to their company Christmas party! Plano makes a nice box too.