Rebedding & leaks
Ken - Don't know your O25, but my '78 O'Day 27 has a balsa cored deck, and virtually everything that was fastened to and thru it has allowed a small amount of water to seep in over the years, causing a small amount of deterioration to the core adjacent to the fastener holes. The best approach is outlined in a West System handbook : it involves drilling an oversized hole ( and removing any rotted core material) and filling it with a thickened epoxy mixture. When the epoxy has cured, then drill the correct size hole for your fasteners, apply the bedding material & refasten the item. If you don't intend (or need to ) remove something again, use 3M5200. In my opinion it provided a superior seal, but it is also an adhesive. 3M4200 is supposed to have the same sealing ability, but is intended for stuff that may be removed periodically. I don't think it is as good as 5200, but that's just my opinion. Silicones, and there are a lot of different formulations available, are wonderful products within their limits, but I don't think they are appropriate for your application.