If the screws are over turned then CA glue will work wonders. Coat the screw with a 'mold release' liquid or spray, put a drop or two of thin CA in the hole and run the screw is. Leave it 'til tomorrow then give the screw a sharp intact type turn to release it from the glue. Put the plate in place and tighten the screw. It may be needful to use a drill and deepen the hole a bit if it bottoms out. If the problem is that the slot in the butt is too large I would do the following. Get some dental floss tape, narrow unwaxed and use it to line the bottom of the cut. This should give you adequate shimming. Also check the pinning on each one as well as glue joints of hammer, shank and backstop and shank. Also check that the flange screw is tight. Newton
This PTG archive page provided courtesy of Moy Piano Service, LLC