Hi Bill,
Here is a
link to the manual.
We have had a similar problem with our Stowmaster All Terrain. Similar to your but is mounted on the tow vehicle.
The problem is likely dirt or eve a little corrosion in the arm It deeds to be cleaned and possibly polished.
First however, pour Simple Green into the tubes from one end and or around the levers. Work the bar in and out for a while then flush with clean water. It may take a while and several applications and flushings to get it clean.
Spray the inner bar with Silicone spray. DO NOT USE SOLVENTS, OIL, WD40 OR GREASE.
If it still sticks you may have to remove the inner arm from the outer (not as difficult as it may look--Once you have disconnected both ends the parts should slide out.)
Clean and the inside of the bushing. DON'T remove much material! I used 2000 grit wet or dry paper which I happened to have. Probably finer than needed. I taped a piece to a deep socket and used and electric drill. Keep the paper wet. A also cleaned and polished nicks and dents from the inner arm. The inner arm should slide easily through the bushing but should not be sloppy.
The problem with mine was scratches and dents from gravel (from Alaska) and road tar from road repairs. Due the to tar I had to use a little solvent but was positively paranoid about removing all traces of the solvent before reassembling. It has worked flawlessly for many months since.
Make careful notes as you take thing apart. A digital camera is useful!
Roadmaster Tech support is also very helpful. Give them a phone call if you get stuck.