Upload & Sell: On
The part the person told me I needed, after I made it clear I needed to replace the SHIFT knob, arrived labelled "YB2-2366 Knob, Tilt." I had understood her to say or imply that it was the same part for both. The TILT knob does NOT fit the SHIFT mechanism. I still don't know what the part number is for the SHIFT knob.
Rather than go through the hassle of dealing with Canon again, and maybe have to shell out another $30 or so after tax and shipping, I decided I could modify it to fit!
(No pictures, but I replaced the "cross-bar" with a narrower gauge piece that fit in the "slot" in the knob, and filed the base of the knob and drilled out the main hole so the screw thread appeared inside the outer part of the knob and could then engage the bushing that has the female thread in to secure the knob. It's a little tight in its gear motion but it is far easier to operate now than it was before all this