The problem is the spool with the small tabs used to align the film during loading. Not the one you slip the end of the film into, but the one before it - you place the alignment notches on the film onto it. A small piece of it broke off, right by the set screw (just to the right of the screw). As a result the film won't rewind.
Interesting ... was it one of the sprockets or something else? If the advance
sprocket is missing one tooth I don't think that will really adversely affect
the operation of the camera since it seems to me that one engages the film
sprocket holes both to the top and bottom sprockes every time.
There is a small screw that rides in a slot of the plastic film advance sprocket. As long as it is able to freely move up when you push up on the
rewqind button that should disengage the sproket from the central shaft and
allow the film rewinding process to take place.
Once pushed up the screw should remain up until you try to advance the film and then it should drop down and the central shaft and sprocket should then turn together. The problem may lie where the coupling "action" takes place but I am not sure right now if it is on the bottom or the top deck of the camera.
andy