After a chat with Catalina
Direct (no shims available), I was directed to West Systems, where I got the audio crash-course in epoxy rudder shaft shimming. Say THAT 5 times real fast....
The procedure is this:
1) drop the rudder.
2) clean rudder shaft and tube thoroughly.
3) drill three holes (1/4") near the bottom of the tube, every 120 degrees.
4) coat the bottom 6" of the shaft with Vaseline and reinsert, without getting any on the walls.
5) mix up a small amount of West System repair epoxy with silica.
6) using a syringe, squirt a SMALL amount of epoxy into each hole - the spot on the inside should be about the size of a dime! Fill the 3 holes so that the epoxy is anchored to the tube AND so you don't leak below the waterline!
7) let epoxy cure, then twist rudder to break bond. If rudder is too tight, pull it out and hone the inside of the tube for a better fit and feel.
Now, I'm not sure if a dime sized "pad" is a long-term solution, but apparently only a little is needed to make a huge change in the clearance. Caveat - if your rudder shaft is bent, the limited clearance will cause the rudder to bind.
If you glue you rudder in place, don't blame me!