I've got a 1969 series I as well. Several years ago while backing into my slip I lost all rudder control- luckily not hitting anything in the process. The next day I took her out of the slip and found that she would turn to one direction but not the other and that the rudder felt"funny". I hauled her out and found a gaping crack on the leading edge of the rudder and the stock just rotating inside the rudder without any effect. Thankfully it was late November and about time to put the boat away anyway.
I pulled the rudder, cut it open and found the tangs that were welded to the rudder shaft had all broken-long story short- I built a new rudder with extra tangs welded on. It's not a particullary bad job, but it does take some time.
Unfortuentely you really can't tell how bad the situation is until you cut it open-unless you have access to an X-ray machine.
Hope this helps,
Tom