I have the same boat, have not had the same malady, can only offer suggestions as if it were mine. First, I'd make a fitting out of a rubber plug and a schrader (tire) valve and pressurize the hull through the drain plug hole. You could do this with an air compressor or even a hand pump while your helper goes all over the hulls with soapy water. If that effort bombs, I'd turn the whole boat upside down and see if any water runs out anywhere. You might even consider filling the hull with water from a hose, adding some food coloring and watch for seeps. As a last resort and considering you think you've got water trapped in the hull, I'd drill very small repairable holes in the top of the hull with the boat upside down to see if you can find and drain the water. Maybe once the trapped water has drained and you patch or caulk where it got in, you'll be OK. Best of luck to you.
OK, this is such bad advice, I can't let it go.
DO NOT PRESSURIZE YOUR HULLS WITH AN AIR COMPRESSOR. It's not necessary and there's a good likelihood you'll explode the hull/deck seam. For real. It doesn't take much pressure to do that - less than 5 psi.
First of all, *something* is blocking the water from running out. There is a small space underneath the pylon shoes that may be blocked by a piece of the plastic bag the flotation blocks are (were) in. In old boats, the plastic gets brittle and breaks up, clogging the drains. In reality, it could be anything - it doesn't really matter.
Strip the boat down to the hulls / frame - remove all the rigging and the rudder system. Turn the boat upside down (in grass) and lift the bows so the water can drain past the pylons. Keep the bows up as you roll the boat back upright so the water stays in the back end. Use a long, thin object (coat hanger?) to fish any objects out of the drain holes as the water drains out.
That should take care of the water in the hulls, now figure out where it's getting in:
Take a vacuum cleaner (shop vac) set on "blow" and have a buddy hold the hose close to, but not completely blocking the drain hole. The object is to raise the pressure inside the hull slightly and allow any excess to blow back out. Now go over the boat with soapy water - anywhere there's a fitting, including where the pylons come out of the hulls and the underside of the deck lip. When you find the leak(s), mark them with a pencil. When you're done, clean off the soapy water and seal up with silicone.
On the back end of the boat, remove and re-install the gudgeons and rudder plug housings with fresh silicone seal. Make sure the o-ring on the drain plugs are in good shape and are slightly compressed when the plug is installed.
That should take care of the problem - without destroying the boat.