Mark _australia said...
what he means is the fin does not bottom out in the cavity. The tapered sides is what makes it tight (it is a wedge shape). So your fin or your box has worn and to make it tight the fin has to go in deeper.
You can put waterproof duct tape, electrical tape or similar on the sides to make it tighter. Keep adding tape until it is flush with the bottom of the board when the bolts are done up tight
sounds about right what's happening..although the coke cans i remembered during one of my first boards that had u.s. boxes-what a shame tho that's the best they could design..plastic will do to..will try it out tomorrow see what happens
and glue can be removed 
just jokin'