I'm curious if the mechanism that moves the piece on the plate is attached to the plate or if it's part of the machine.
They don't show the underside/plate removed on the Juki site, but the photos above look exactly like a manually-operated (lever) version of the Janome 7700's APC plate. On that machine, the spring that operates the little rectangle that switches between single hole and zig zag is somewhat fragile. I've been careful with the one on my 7700, but looking at the mechanism you can definitely see wear on it from switching back and forth.
Michelle