O.K., got it all apart now.
Think I can safely say that if your window won't move but your motor runs, the problem is with the cable connections.
There's two nylon parts which affect this. One is the top end piece along the glide rail around which both loops of the to-fro cable go around. The second piece is in the vertical middle of the glide rail and attaches to both the glass and triangular glider which slides along the rail. It's at this middle piece where the two ends of the cable meet, but from opposite directions, one up, the down. So, when the window will move only one direction, it's that side of the cable end which has pulled loose. If both directions fail, while the motor still runs, then both ends have pulled loose.
I don't know wheather it's contributing or cause, but my top end piece had sheared in half through the pulley, spliting off one side face of the nylon piece. Together with this, the UP side cable had pulled loose of the middle piece.
By 'pulled loose', I mean broken through the hole which holds it. The nylon piece busted there. That piece also happens to be pressure fit with a bearing to the glider piece, making replacement all but impossible. It requires a new glider piece (the main triangular metal piece which bolts to the glass and glides on the rail). And, I doubt that piece is available by itself. More likely, the entire regulator is what's required.
The motor is nicely seperated from all this and attaches independently to the inside skin of the wall itself. Loosen two bolts, remove another and it comes out through the hole via sloted bolt holes.
I also have a relatively minor problem in my motor, I discovered. And, it could be what caused the entire problem (especially since this window is seldom used). The cable near the spool end had wrapped up over the edge of the spool and tended to drag the spool as it turned. Probably a condition which existed from manufacture. It didn't loop out, just a peak bend up over the edge. The tolerance between the spool and the surrounding housing is narrower than the cable thickness, so it drags.
Anyway, when the stresses get too large in any place, the entire system tends to self-destruct. How many pieces break and where is random.