A build up of deposits in the rudder-post tube distorts the Delrin bearing causing it to “squeeze” the rudder post. The deposits have to be removed. On mine a few years ago, the boat had to be hauled and the rudder post pounded down from the top to get it out of the tube so it could be cleaned, etc. This was after soaking with lubricant the post in the tube for a couple of days. Been fine since then.