T-Bird has it right. For clarity, note that what created the crack was probably the screw at the bottom of the tuner. It appears that it may have been installed without drilling a pilot hole. That was like driving a wedge into the wood and forcing it to crack. It's poor installation technique.
Use the screw which is in place to hold the crack open - then add glue (a syringe is good and you can add a bit of water to white glue or Titebond to help it flow). When the crack is full, remove the tuner and screws to allow the crack to close. Wipe off excess glue with a damp cloth, then pad the jaws of a clamp and clamp it overnight. Don't kill it with the clamp, you only need a firm grip.
When T-Bird said "open up" the screw hole he means to use a drill and drill a pilot hole for the offending screw before re-installing it. Then the screw will not exert undue force on the wood and cause it to crack again.
Super glue will work, but it is extremely unforgiving in terms of working time (it's essentially instant so you get no time to position or work on the wood), sticks to everything and requires acetone to remove, and may be difficult to get throughout the crack area.
"The best way to tell a lie is to tell the right amount of the truth, and then shut up." Robert A. Heinlein
Last edited by Pilgrim : 01-13-2013 at 08:43 PM.