The hulls are made in two halves, the top deck areas are cut out, the halves are joined, the daggerboard wells fitted/finished, the exterior seams are refinished, and then the decks glued in place.

My F18 had a similar deck leak - but your repair options depend on where and how severe the deck leak is. If it's forward of the main beam, you probably want to do the following because the decks provide an important structural component to the boat. I've had a deck before that could be lifted with a fingernail - it was leaking badly. I fixed it by very tightly masking off the hull and the deck around the seam and working in epoxy with some microballoons. I would push the deck down, and using a syringe, apply epoxy to the joint, then ease the pressure off the deck. I did this several times until I felt the joint had drawn in plenty of resin. Then I used a series of wood blocks and ratchet straps around the hull to apply light pressure to the deck. It has held up fine. If you have a slight leak behind the main beam and it's relatively minor, you can seal it using 3M 5200...note that 5200 cleans up easily with mineral spirits leaving a very nice smooth finish.

The daggerboards have a potential to leak in a couple of areas. The first (and easiest to fix) is where the daggerboard might wear through the back of the trunk at the top of the slot. Look to see if you can see an opening there. Simply fill this with polyester or epoxy resin mixed with microballoons or milled glass fibers. You might want to mix in some aluminum powder because it will help with future wear and abrasion resistance. The second potential leak is the sealant used to seal the top deck to the daggerboard trunk. If you pressurize the hull (NOT TOO MUCH PRESSURE - use the exhaust of a vacuum cleaner), lie on your back lookup up the daggerboard well and spray soapy water inside the well.