Looks like yours is a 1984 (like mine was). The rudder rotated around a metal pin (rudder post) that fitted down into that grommet hole and locked into place. The post had a button in the center of the top of it that, when pressed, was supposed to release the post so you could pull it (and thus the rudder) out of the hole/socket, but mine never could be released. You should try to get together with bilnik to see what the rudder looks like and how it works.