I have just finished restoring a dash bezel that had the same problem, including broken corners, and holes drilled in bezel, for whatever reason. I repaired using a fibreglas reinforced polyester filler(kitty hair). I first used masking tape on front of bezel to create a smooth finish and to eliminate any unnecessary sanding. I then carefully filled the void with filler from the back side being sure to eliminate air holes and then left a thin layer of filler on back side about 1/2 inch either side of area being repaired to provide added strength, that old plastic needs it. After curing I carefully sanded with my Dremel tool, drilled new holes and counter sunk the front side to accomodate the correct type screw. Hope this helps, it seems to have worked for me. John