Update: I took off the two keepers with the help of my FIL, cleaned the old sealant off the surfaces, screws, and nuts with various nasty solvents, working behind a box fan acting as a fume hood of sorts. I bought some 1" self-stick velcro, cut a strip of the loop half down the middle with a knife and straight edge, and stuck that onto the bottom of the sliding hatch.
We rebedded the strips with butyl tape, just around the screw holes. With the flat head screws just short of flush with the strips, I wound some butyl tape around the heads, stretched out into a thin strand like bubble gum (that stuff is super stretchy), then pushed them the rest of the way in. The nuts were tightened from below so as not to disturb the sealant under the screw heads. Three screws were actually wood screws, as there was no access to the underside, but the tape seemed to not get pushed out from under the heads.
I didn't repair the worn gel coat, as no water was entering through the worn spots, and they weren't even worn enough to penetrate to the FG, as far as I could tell.
I'm happy to report that after two periods of very heavy rain, lasting a couple of days each time, NO water has come in from under the headliner. It used to drip off the bottom edge, over the table (ruining the map that was under the clear plexi) and on the port side soaking the seat cushions. Not a drop, and I couldn't find a damp spot at any of the screws (the plugs are still soaking on soapy water to clean them up).
I used to get some water on the electric panel under the winch on the port side, which I suspect came from the crappy way the jamb cleat was mounted (inboard screw just sort of kissed the keeper strip, so the hole was just 'there', where the water runs), but it's dry under there at the moment. The real test of that would be with the dodger removed, though there was plenty of water under there from the wind driven rain.
I still need to rebed the mounts for the short struts on the Dowsar dodger (anyone with that dodger knows what I'm talking about), as they're not through-bolted and are loose. I'm sure some water gets in through there. Maybe I'll drill those holes out, fill with epoxy, and rebed the mounts with butyl tape.
It was a LOT of work, as many of the nuts on the starboard side were buried in the FG, and were a real pain to get access to for a socket. A drill with an adapter for a 1/4" drive socket was a huge help. But it was worth the trouble.
The interior is finally dry, and no more boat smell. I had also fixed a major water entry point where the steering cable enters by stuffing the space with (what else) butyl tape, detailed in another thread. Now that I know that's where the big water entry problem was in the stern, I'll look into a boot for a more permanent fix, but the sticky tape is actually hanging in there so far. Not a drop back there, even after all that rain.
Thanks to all for the insights.
Oh, and to Kevin's point, no more screeching.
