Well first off, was the watch purchased through an authorized dealer or a grey market source like Amazon? If the answer is Authorized, I think you'll have to ask Seiko about it. I know that a lot of companies wont repair screw down crowns as that's often an issue caused by user error. If the answer is grey market, then there is a pretty good chance that you'll be high and dry. Either way, the answer is to call whomever is appropriate and ask them.
Was the crown that bad from the beginning, or has it gotten progressively worse?