I assume the tank was a Private transaction, like CL?
If it was ebay, they have purchasing protection, and I would get my money back. If it was CL, no such luck charlie. Sorry to hear about your problem, nothing worse than waking up to a wet floor and then realizing where it came from.
I'd contact your LFS and see if they have a custom builder they work with. He might do a re-seal fairly cheap. With the supplies, and the knowledge, sealing should take almost no time, and only tie up his equip for a few days.
GL