Your problem got me curious so I did a search on keel bolts and there
is a plethora of info on the subject of inspecting and replacing keel
bolts. Owning a 28' boat, I have never had this problem because my
ballast is internal to the hull of my S2. Considering the difficulties
with bolt-on keels, why do they seem favored over good internal
ballast?
Now I cant stop and will become obsessed with finding a way to inspect
keel bolts...