RoadMaster Sterling tow hitch arms stuck?

Hi all. I have an old Sterling tow bar. Its arms are supposed to freely slide in or out. They don't except with lots of force or hammering with a rubber mallet to get them to retract. I was once told the problem is that the rubber/neoprene bushings inside swell with time and choke onto the stainless steel slide arms. I replaced these bushings a number of times over the years. It usually fixes or improves the problem but it always comes back in about a year. I have only used silicone lubricate as stated on the RoadMaster web site. They are stored in the garage when not in use. The last time used, they worked fairly well when put into storage. I got em out for a trip and the arms are stuck tight? Any way to fix it so it stays good?:h