try spraying wd40 around and inside from the top of the rudder allowing it to seap into the internal bearings and o rings to clean and lube them up. This should allow it to loosen up and hopefully give it some more life. You might have to replace the rubber/plastic o rings that seal the boat from the water. If you have had it out for a long time it might be good to replace the internal rubber. If its grinding sticking and making noise you might have to change some sprockets or chains or etc...
