I bought a 14 (1970 as near as I can determine) in pretty rough shape a couple of years ago. One hull was much heavier than the other, with no obvious water in it. So I installed a hatch and stuck a light bulb in there for weeks. It worked - now the hulls are within 5# of each other. Used this link for advice. I put it behind the front pylon, but you have to miss the foam block inside the hull and the pylon base. Lots of discussion on the boards about locating the hatch.http://www.thebeachcats.com/news/29/ins ... cle29.html
Also put in new drain hardware and plugs. Here's one thread:viewtopic.php?f=14&t=7828&hilit=installing+hatch
Let us know how it goes.