I have a 1982 Dufour 2800, and while this is a much smaller boat, it has a similar spade rudder to yours. I discovered to my cost one inadequate part of the design of what is generally a very well-built and sturdy boat when the rudder fell off while sailing in Bantry Bay ten years ago. The rudder has nylon bearings top and bottom of the shaft, the bottom one being of course just above the top of the blade. While the top bearing was sturdy and substantial, we discovered while disassembling the rudder that the bottom bearing was very thin indeed. I’m not sure whether it was actually split as shown when the mishap occurred, or split when it was taken apart.
I attach some photographs which will show what I mean. I hope that this is helpful.
By the way, We were lucky to be some way from the shore when we lost the rudder, and were rescued in time by the Bantry Inshore Rescue boat, and we found a fantastic local marine engineer who did a great job replacing the rudder, with the substantial new bottom bearing which is shown.
Robert Brown