same problem...
I have just about the same problem on a 1979 O'Day 27. The lower shroud chain plates are embedded in the deck. You have the top skin (deck), balsa core, the chain plate (that is the square you see in the salon and head) and the lower skin. Then you have @1/4" space and the liner you see inside the cabin.Your fear is real, I found out about my problem when the starboard rear just about pulled thru the deck last October in @ 18knot wind.I contacted several yards, they all said it would cost between $6K - $8K to fix, the deck has to be removed. I dont know how handy you are but I'm doing the job myself (with a boat builder looking over my shoulder) it should cost me @ $500 in materials + my time. In my final solution I am replacing the balsa core with a hitech composit material (the builder I mentioned uses this stuff on one design boats)resin & glass. I agree, these shroud chainplates go down as a big screw-up on O'Days part (notice the 28' has tension rods to the hull)My thing was I couldnt sell the boat in that condition, I wasnt about to put that much $$ into a boat thats only worth $10K, so that left me with, either do the work myself or give the sawsall a workout.Good luck & let us know how you make outRichJ