I had the same problem with my CT22. After handing in the unit for repair, the tech said i should be more careful twisting the reostat knob, and I had broken it by force.
I had no memory of ever doing so, and had only used the knob a handful of times with my sanders. I take meticulous care of my tools- especially the blue/green ones, but I didn't argue- just thanked him for the free same-day repair job. For the record, my CT22 was made in 2005 and the repair was done last Fall.