Thanks for all the replys. Here are some pics of the patient.
The chainplates are mounted to the frames inside the double planking, indeed, I would imagine they were installed before the planking. Removing them would one nasty job. And ultimately, I think , not necessary. The only movement seems to be in minor flexing ot the tang that protrudes through the deck. As it stands now I have stuffed around the tang with oakum and paint. I then used Boatlife as a seam compound which seems to have been a mistake as it did not adhere to the paint(which was admittedly still tacky).
With Hurricane Dan bearing down on me, I decided to close the holes with plumber putty until this week when I will test to see if the caulking stopped the leak and what would be a suitable seam compound. Suggestions?