Did you review the other thread on this subject?
https://www.hobie.com/forums/viewtopic.php?f=78&t=54197Who did you speak to? Did you try your dealer?
I would check the internal lines for possible a obstruction or foam block issue pinching a line. Release the line and pull the rudder down by hand. If you press it up into the hull, will it pop down on its own with the line loose?
Check the area under the black cover. A number of years ago we had a kit to re-route the line due to it cutting into the plastic.
If you can, look at a current model for updated routing.