Saturn Repair: Saturn 96 rear window work intermitent, square blocks, rear windows

Question
Both Power rear windows work sometimes.  If they don't work, still hear motor work the lifting arm.  Took off one of the door panels.  window Lifting arm has ball on the end, and originally the ball fit into round hole in center of a plastic (nylon) square block.  The square nylon block rides in the track that the window sits on.  The nylon block is split vertically in 2 halfs (broken) and the ball rides directly in the track.  If the window is raised or lowered half way the ball will not stay in the track. Why? The window arcs out away from the ball half-way up.  
To reset the ball into the track:
1) Raise the arm (by operating the switch as if raising the window)
2) Manually push the window down (open it all the way)
3) Lower the arm (by operating the switch as if lowering the window).
The ball will pop back into the track when the arm reaches the bottom, and the window will operate - fully up the ball will stay in the track - fully down the ball will stay in the track - stop half-way and the ball will pop out.  It doesn't pop out when going full up / down because the edge of the ball is hooked on the track edge.
So, here's the question:  All I need to fit this are new plastic (nylon) square blocks.  I can take the old ones out and put in the new ones  - slide the old ones out the end of the track.  Where can I get a couple new nylon square blocks?
P.S. I saw there was a question from someone else about front Saturn windows not operating all the time - could be the same problem.  I think as both my rear windows have failed, this may be a more common problem.

Answer
Brian,
 In a nutshell, no.  If you can find those nylon blocks, more power to you.  I have not seen them as of yet.  The only way that I know to fix it is to replace the regulator on each side.  You could possibly build those nylon blocks out of some hard (ABS) plastic.  That would probably save you $200 in parts.  Let me know how it turns out.

Chris