Screws do not hold well if screwed into end grain compared to across the grain no matter if it is plywood or wood. That is a fact of life and it never should have been constructed that way. My fix is to use wooden dowels but in a different way. You can use the same screw holes so don't have to put more holes in the trim. get some 3/8ths or 1/2 inch diameter dowels and the same size drill. mark where the screws enter the plywood and drill your dowel holes into the side of the plywood. Cut the dowels to match the plywood thickness and glue into the holes; the dowel should have a snug fit into the holes. Now when you re-install the screws they will go into the side of the dowels where they will hold much better. Jim.
