use the exhaust of a shop vac to blow air into the hulls - don't seal up the hose - just let it blow into the hulls to build a little pressure. Spray around all the potential leaking areas with soapy water and look for bubbles.

I recently had a leak in my daggerboard well that leaked more and more every time out. To fix it, I taped the bottom of the hull around and over the daggerboard trunk with packaging tape. I then cut out the daggerboard opening in the bottom with a razor blade. Using epoxy thickened with cabosil, I filled in the hole. Then, with the daggerboard also protected with packaging tape, I inserted it into the well to hold the shape of the opening. Once cured, a sharp knock with my palm knocked the board loose and I peeled off the tape cleaning any residue with acetone. No more leaks!