It sounds like the holes holding the rudder to the mount are worn. If memory serves me correctly, there are 2 brackets holding the rudder to the shaft that locks into the lower rudder mount. Remove the rudder, fill the existing bolt holes with epoxy and/or a piece of dowel, then re-drill the top hole and slip a bolt in temporarlly. Determine the proper angle (120 degrees min.) between the leading edge of the rudder and keel (see ISCA rules diagram at the bottom of rules), mark and drill the bottom hole. Insert a new bolt and tighten both bolts and you should be back in business. While the rudder is removed from the mount, you may want to refinish the blade with new varnish and/or fiberglass. Rule 3.3.2 allows you to bush the holes to strengthen (reduce wear) them. The ISCA rules are found on the National Sunfish Class page, left column. Good luck.