Well I could just cry - $90 later and the stitch selector for A-J has some movement (so yay!) but when I opened it up, that finger STILL isn't in the collar slot for the K-S side. The finger is now resting on top of the collar and goes into notches above the collar. So I can't move the knob past O.
I still suspect there is gunk below the K-S collar and the collar sticks in it, and refuses to travel up the shaft.
Kicking myself for not moving the knobs in the store. Just took his word for it. (He had stitch examples he had done with the machine.) It will be a two-hour round trip, but at least I expect he will stand besides his work.