Friends of mine have a Catalina 470 that lost steering south of Bermuda and took a $6,000 tow . They had a new rudder made by Catalina, installed in Bermuda and are now in the BVI. He did an autopsy on the rudder to find out what happened. The rudder post was constructed out of two pieces of SS with a welded collar down inside the rudder. Over the years water had gotten to the weld and crevice corrosion did the job. The rudder didn't fall off, it just wouldn't turn. Not sure how one can check for this, or prevent it.