Re: rudder failure?
The best way I know to test for structural integrity is to do the "tap test." In other words you literally tap the surface with your knuckle or a screwdriver handle, or the like and listen to the way it sounds. This works for cored decks, hulls, and so on. If it sounds like a dull thud, then it is wet, rotted, etc. It should resonate slightly, indicating there is good wood in there. I'm not sure about the 27, but the 22 has a ply core in the deck and rudder. If your rudder has had ample dry time and sounds solid, glass it up and you should be fine. If not, you'll have to cut one side, clean and re-core, then glass it back together.