A balsa-cored deck forgives a lot, right up to the point where it forgives nothing.
Finding the wet ones
Tap along the deck with a coin. The dull patches are where you start, and they are almost always around a fitting.
Overdrilling
Drill the core back, fill with thickened epoxy, redrill through the plug. Then the fastening never touches balsa again.
Bedding
Butyl for anything you might undo, sealant for anything structural. Torque it down in two stages a day apart.
