sticky sterling towbar.

Roadmaster has complete manuals for all their devices on line in .pdf format. I would download the appropriate one for your towbar. I bought a used Sterling All-Terrain and had the problem you described. I called Roadmaster and spoke with one of their techs who was very helpful. He had me disassemble the towbar and do a little sanding of the plastic bushings that make up the inside bar. I then cleaned the bar extensively and lubricated it with ONLY silicone spray.....anything else will only attract more dirt and grit. I still had some difficulty with the bar being difficult to move into position. We took a long (8000 mile) trip last year and within the first few days of the trip the bar was functioning like a new one. Guess it just took awhile for everything to smooth out but now it works just fine. I used emery paper on the tow bar and shaft and I also worked the inside tube of the towbar using a long screwdriver and ran the emery paper there as well.
Seems lack of use is just not a good thing for these devices. Hope this was helpful.