If surfaces are rubbing or interfering where they should not be, like where you applied the fine sandpaper. Clean those surfaces and apply some Dykem (layout fluid) or felt tip marker, work your bolt/lever a few times, then check where the Dykem or marker has rubbed away. Not sure how good your eyes are, I have to use a magnifier much of the time to see the rub marks or transfer. In more drastic cases of poor fit or finish, Prussian Blue or lipstick is a good transfer/witness marker.
smokeywolf