RE: moisture content of teak core
Albin, I'm sure there is a lot more than 15% moisture trapped deep under the extra fibreglass, marine ply stiffening, then further layers of glass cloth/resin laid over my decks when the old leaky teak decks were replaced before I bought her, but there is no sign of it whatsoever, unless I drill a core out for a deck filler or similar, so my advice - don't worry about it, as long as there is nothing leaking inside. Replacing internal teak, stained/damaged from before the deck restoration - now that's another whole project - best prevented. That where to spend the money - removing old teak and sealing that deck, but from what you say, it's probably not worth it ripping out all the core. Just get that top deck surface waterproof and non-slip.