For a permanent repair :
Remove the tuner.
Gather tools- a (sharp) single-edge razor blade, small bottle of wood glue (Elmers white glue will do,) sharp pencil, small tack hammer, small drill, toothpick.
A round toothpick will work best.
Insert one end of the (round) toothpick into the screw hole all the way, it should be snug & not wobble. If it is not snug, snip-off a tiny bit from the end of the toothpick and re-insert, repeat as necessary so the toothpick is a snug fit. With the toothpick pushed firmly in the hole, put a pencil mark around the base of the toothpick where it exits the headstock. Pull the toothpick out, take the razor blade and score the toothpick around the pencil line, but don't cut the toothpick all the way through. Coat the end of the toothpick in wood glue, place it into the screw hole, seat it down snugly by tapping the exposed end of the still whole toothpick with a small (tack) hammer. Wiggle the toothpick back & forth a little, and it will break-off cleanly at the base, where you scored it. Allow to dry for a couple hours. Before re-installing the tuner screw, re-drill a pilot hole first (about 1/4" deep) with a tiny bit (1/3 to 1/2 the diameter of the screw.
