I am not sure if this will help but i find that when diagnosing physical issues that the slower I move something the better I can feel the subtle changes. Speed of movement gives inertia which makes things "easier" to move. If you move super slow sometimes a part that moved stiffly will stop at the bind point.
One other idea, the only machine that I have had that had a pillar mount stitch regulator issue it was because the screw/bolt under the hand wheel was loose...
my .02