There isn't anything. If you have leaky teak decks then the only way to stop them leaking (if at all) is to re-caulk and re-fasten. If they are traditional laid decks straight onto deck beams then you may not ever be able to stop all leaks because the whole structure tends to move. If they are teak laid on a substrate such as ply or GRP and water has got in then at some time you have to strip the whole lot off - and then probably best to make good the substrate and sheathe with epoxy and glass.
Can I ask:
- do mean the decks are made of teak? If so forget the following questions.
- when you say deck leaks do you mean water getting under the teak or through the deck into the cabin?
- what is the deck material (GRP/wood/steel)?
- is the teak deck laid on that material or marine ply?
- whatever the teak is laid on are the the screws still in place or have they been removed, holes epoxied and teak plugs put in?