"I just finished my tenth round of skeet with the gun and broke it down to clean it, the shim is gone !! Barrels off face again a complete waste of time. I deserve it for putting my faith in glue.
"
Working on a Sterlingworth and my shim disappeared. Could not find it. Took action back off the gun and it was under my floor plate when I took the stock off. So shim did not vanish, look down in the action or it fell off onto the ground. You can just place the shim on the roll pin and place the barrels on top of it. Then when you disassemble, remember it is there. I use red automotive grease for hinge pin grease and the shim is usually stuck there.
Of course the only permanent way is to have the hook welded up. As stated a professional job.