Yeah thats because when the filler gets truely hard it does sink, that why I've left mine s long so the filler has plenty of time to go rock solid and im lucky because im able to bake all my repairs, its also better to prime it twice so you can see where its sank when you block it down so you can apply more filler of need be! yeah it is i can screw the nuts in but i cant fit a socket in there to tighten it up so i need smaller nuts