I had a similar problem and solved it by removing the wooden capping (sand keel) routed a groove the length of the hull between the 2 halves replaced the keel strip bedded onto sikaflex and screwed in place and then drilled a number of holes internally into the groove and poured epoxy down so that it ran along the length appearing at each hole to make sure that the groove was filled the theory being that the liquid epoxy would find its way into any voids as it ran along the groove if you could pump the epoxy into the area then the extra pressure would make sure that this happened. This process cured many problems however I still had some leakage which was solved the other year by stripping back the hull to wood then checking that any screws were in good order replacing and filling where necessary and then coating in flexible epoxy from reactive resins (discount available to assossiation members) and finally using their copper antifoul.
hope this helps you also need to make sure that there are no obvious areas of delamination which would need a proper repair.