I saw this post only after replying to the other thread about this problem... Glad you found your answer.
For those who were trying to help - on this boat, and I believe she has a 1993 26S not X, the keel pivot bolt cannot leak into the cabin, as it can on the non-water-ballasted boats. The keel bolt ends are fully contained within the ballast tank, and the two plates are the access ports that are used to reach them. This was used on late 91 models through the last of the 1995 production boats. So one thing to not worry about there.
The downside to that is that you have two 4" diameter open inspection holes on the top of a flat ballast tank which can leak if the inspection plates aren't sealed well. Other than that, the ballast tanks are VERY thick fiberglass on these boats, and that is another thing I wouldn't worry about at first. Kinda the last resort to look at.
Beyond that, the only factory holes open to the cabin are the vent and the fill valve, where the shaft sticks out the top. You found that the plug was leaking...excellent!
So Pam, I think we're all making the assumption that you know how to tighten the rubber plugs you use to stop up the vent hole under the stairs... Not at all condescending, do you know how to adjust them to get them tight enough, or as tight as you want them? They are easily adjustable.