Sean, I am not sure how that one is attatched, but I do have a couple of possible solutions. You could try a 2 part epoxy to glue it back down, might work for a little while. If you have grooves under the rail take it off and mount scope, may have to reblue under rail. Gamo just started selling the clamp on rails, get one and swap them out, probably the best of the 3. HTH wish I knew more.
Mike