This article (originally submitted by Chris Burti) is based on using a polysulfide type of bedding compound. I prefer to stick with that, except using butyl rubber for sealing the deck plate and screws. (W.Updike 10/2016)

Re-bedding Chain Plates

1.  Move your cushions far away from the big mess you are about to make and get the table out of your way.

2. Remove the shroud. (Do one side at a time. Use a halyard to a stanchion base to replace tension from shroud while rebeding.)

3. If the mast is still standing, have a beer.
4. Remove the strut. (this is the bar between the deck plate that runs behind the settee and is attached to the top inside the hole behind the settee.) Remember the sequence and position of the spacer and washers at the bottom of the strut. Mark the spacer so you know which side is up. A crows-foot socket makes loosening (and tightening) the nuts on the bottom of the strut a little easier. The strut holds a bit of tension between the deck and the beam that is built into the liner. Notice how many turns it takes before the upper nut on the bottom of the strut comes loose and releases that tension. This will help when you reinstall and re-tension the strut. Mine came loose after about 1 1/2 turns.
5. Remove the 4 phillips head thru-bolts. The threads on mine were a mess so I had to purchase new ones, 1/4 x 20 x 1.5″.    
6. Remove the tang (step on it).
7. Mask the deck around the trim plate so clean-up after caulking is a little easier.

Tip: For a neat finish. After you remove the deck plate, remove the old caulk from the deck, lay some masking tape around the deck and over the edge of where the plate lies. Now, replace the deck plate and with a knife, lightly score the tape around the edge of the plate.  Remove the plate and peel up the tape that was under the plate. When you caulk and replace the deck plate, let the caulk squeeze out from under the plate and cure for a day. Score the caulk around the plate and remove the excess caulk and the tape.  Clean job, no caulk left on the deck.

8. Pry the trim plate off of the deck.

9. The hole in the deck is larger than the tang and is filled with caulk. Clean out all of the old caulk.

10. the deck has a wooden core, clean out any rotten wood, let the core dry and fill the void with an appropriate filler. (see below)

11. Clean all surfaces with acetone.

12. Install the tang with the 4 screws but without the trim plate. I didn’t use any caulk on the underside of the tang. If the topside is sealed there doesn’t seem to be any purpose to it. If the topside isn’t sealed it would just mask the problem while your deck rotted.
13. Fill the space around the tang with Life-Calk or other appropriate flexible adhesive/calk, and et it cure overnight.
14. Trim the dried caulk around the tang so that it is flush with the deck.
15. Remove the phillips bolts
16. Put a heavy bead of caulk around the tang. (Use of butyl rubber for beding the deck plate is appropriate. Ref. Compass Marine site for info. Be sure to properly chamfer the deck holes.) 
17. Put some caulk in each bolt hole. (or wrap the bolt with butyl rubber, see #17)
18. Put a bead of caulk on the deck around each bolt hole.
19. Place the trim plate in position and press it down firmly to force the caulk up between the plate and the tang.
20. Put some caulk under the head of each bolt and push the bolts into the holes while pulling up on the tang. Don’t push the tang down and ruin the seal.
21. Tighten the 4 bolts only until the caulk shows all around the plate. Do not, at this time, firmly secure the 4 bolts. It would help to have someone on hand to assist with this step but I managed without. (This is especially appropriate if you are using butyl rubber. The material is stiff and will require some time to ooze out under pressure.)
22. After the caulk has cured, tighten the 4 bolts, clean up the caulk, and remove the tape.
23. Attach the strut. Tighten the upper nut until just snug, and the approx another 1 1/2 turns.
24. Attach the shroud.
25. PauHana, you’re done.

 

Step 10; Comments of Warren Updike March 2014

You will likely find that the plates go through the deck and balsa core. Don’t short-cut the project, do take time to remove the core and fill the void. To remove the wet and damaged core: bend a nail to 90deg angle and with a drill motor and the bent nail, run it through the deck hole around  the balsa core space thus removing the core to the depth of the bent nail extension.

 

Now, if it is still wet in there it must be dried out. Squirt alcohol into the now relieved space and allowed it to dry. Some have used a product called “Get-Rot” that may help. One may also encourage drying by running a space heater in the cabin for a couple of days with the bottom of the deck hole open. If leaving the boat, cover the deck opening with duct tape in case it rains. It could take 2 or three days for the space to fully dry.

 

Once dry, tape the hole from the inside and use unfilled epoxy to flood the void in the deck. Then poke a hole in the tape from inside and drain the epoxy back into the cup. Add a filler to the epoxy to the consistency of peanut butter. Force the filled epoxy into the void in the deck leaving it flush with the surface of the void. Let this cure, then proceed with the rebeding. You won’t be sorry you took the time to do this as you will have no further risk of damaging the balsa core.