1. Find the leak
Water tracks along the underside of the deck, so the drip below is rarely under the leak. Dry the area, then have someone hose each fitting in turn while you watch inside with a torch.
Tap the deck around the fitting with a plastic mallet. A dull thud instead of a sharp ring means the core is already wet and needs drying before you seal it back up.
2. Remove the fitting properly
Undo the backing nuts, then break the old bond by twisting the fitting rather than levering against the gelcoat. Bag and label the fasteners.
Scrape every trace of the old sealant from both the deck and the fitting. New sealant will not bond to old sealant, and this is why most re-bedding jobs fail second time round.
3. Seal the core
Over-drill each bolt hole to about twice its diameter, rake out 5-10 mm of the balsa or ply core, and fill the void with thickened epoxy. Once cured, re-drill the correct hole size through the epoxy plug.
This creates a solid, waterproof collar so that even if the sealant fails again, water never reaches the core.
4. Bed and fasten
Mask around the fitting, chamfer the top of each hole slightly, and lay a generous bead of sealant on the fitting plus a ring around each hole.
Tighten only until sealant squeezes out — do not crush the bead. Leave it for an hour, then fully tighten. Trim the cured squeeze-out with a sharp blade and pull the tape while sealant is still soft.
Common mistakes
Using silicone: it fails on deck and prevents anything else bonding afterwards.
Torquing the bolts fully straight away, which starves the joint of sealant.
Re-bedding over a wet core — dry it out first or the rot continues underneath.