Most of the smaller boats <26' have chain plates similar to the three in this picture. There should be a plate that surrounds the chain plate
. That needs to be removed and the sealer that is under it needs to be cleaned out. And then squeeze a nice heavy bead of sealer (I use 3M-4200) around the chain plate.
With the sealer still wet, replace the surrounding plate and fasteners and clean up the excess.
If your not able to un-step the mast
, you'll have to do one at a time, unlike the picture. Also with the surrounding plate removed and cleaned out of old sealer, check for a wet core
. One way by pushing on the deck
around the chain plate to see if it's soft. another by a moisture meter. Since it's been leaking let it dry out or use a hair dryer (not heat gun) to see if you can get it to dry out.
That should keep you busy for a while!