[high_vacuum_house]

I have one though not to hand at present.
Could it be that if both the spigot rollers are driven together by the tuning knob shaft maybe that they are misaligned by the gearing to the tuning knob by a tooth or 2 to cause sprocket hole misalignment. I presume the tuning mechanism hasn't in the past been dismantled and reassembled? How is the calibration?

Christopher Capener