When my beloved guitar suffered an accident and developed small cracks in the top, my brother the expert told me the following:

1. The first question is, does the crack go over a GLUED JOINT? If it does, you need a professional. If not, go to step 2.

2. Chances are, the cracks are following grain lines in the wood. If so, stop them from propagating by drilling rounds holes at the ends of the cracks. Make the smallest hole you can. (My husband and I did this together, using a sewing-machine needle for a drill bit.)

If you wish, you can then buy wood putty and patch the crack.

3. We did this to my guitar ten years ago or more, and it's been fine ever since.

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For the other screw, try Bill D's 'small dowel' solution. Bear in mind that the smallest dowel around is a toothpick.