The story as understood, was that the rudder had been dropped twice for work. As we peel back the paint the rudder might have a different description of events. The most common reason for dropping the rudder is water intrusion. In this case, when the rudder is removed one face is cut away to scoop out the wet foam core. The rudder is dried out and the steel is inspected and pasivated. Then the rudder is reassembled by filling the shell with expanding foam, shaping and glassing.
As described in the diagram above the steel frame is encapsulated in fiberglass mat and polyester resin before the foam is added for shaping. So if water had intruded past the outer shell it may have never reached the steel.
After removing most of the paint we did not see any evidence that the rudder had been openened. There are several blister repairs but no definite seam on one side or the other.
We opened a hole near the bottom of the rudder and attached a vacuum pump. After several days of pumping the rudder was dry and we injected a two-part polyurethane foam.