Im a ex-16 sailer, but i sailed them for a few years, and it sounds to me like you've got water in your mast, this is frequently a problem with the older boats. if you cant get and water out (tipping the mast from end to end and listing for water is thebest way of telling) then you just have toi harness hop, are you doing this already? this is where the crew stands on the spreader bar of the other crew member who is trapezing off the righting line. if you do find water then just drill out a rivette at the end of the mast and drain it, then seal it up again, u are unlikely to fing the source of the leak and to do so requires a lot of hard work and time in the garage. best of luck with your righting efforts!
Drew