OK, those tend to be the more difficult and expensive guns to fix.
I doubt FS will touch it in-store, but can probably suggest a gunsmith to take it to.
Is it an antique?
I would call North Shore Firearms in Middleton. They look to be more into the Shotgun World than Four Seasons. They carry a lot of newer and used good grade O/U's. So they may have a better answer. But then again Four Seasons may have the better answer. Just a suggestion based on Inventory.