Your problem might not be dirty contacts. I recently found that my cam barrel had deteriorated and actually had shrunk. The end of the can barrel serves as a bushing that fits into the mounting bracket. The diameter of the bushing was smaller by more than 0.01 in ( 10mils). Consequently it was too loose. In addition, the cam lobes were also smaller in height. With the overall diameter shrinkage, the bushing was loose and the cam lobes were not applying sufficient pressure to make firm contact. Fiddling with the knob to make contact is a clue that the cam barrel is loose fitting.
