Hi Alex, is your fin box wobbling in the board (loose fin box), or is the fin is wobbling in the fin box? In both cases you should check:
1. check for a crack inside the fin box.
2. check if you can move the inside of the fin box around (box is fixed on the top laminate, but loose inside where it sits in the foam)
If that's the case, you have to replace the fin box. This is how it's done:
http://www.boardlady.com/anatomy.htmhttp://www.boardlady.com/repairmenu.htmhttp://www.boardlady.com/tuttlebox.htmhttp://www.boardlady.com/jppowerbox.htmhttp://www.boardlady.com/fcsinsert.htmYour fin box might also be cheaply mounted directly into EPS, without a layer of dense foam around it. As yours is a production board this could well be the case. Then you should also replace the fin boxes to get rid of the problem, or ignore it and live with a bit of wobble.
If for whatever reason the box is ok but the fin doesn't sit snug (worn out - not very likely), put electricians tape on the fin until it's snug again.
cheers, tungsten