Both of my front windows (nylon wheels) went years ago (when it was 3 or 4 years old). I replaced the mechansim once on the drivers side (for some exorbitant fee).
When the passenger one karked it, i just bent the 'scissor arm' with the broken wheel in towards the channel. That way, the 'shaft' of the broken wheel acts like the wheel in the channel (except it slides now). I put a bit of grease on the channel to help it slide...
I had to bend the arm to make sure the shaft stayed inside the channel and didn't pop out, leaving the window behind...
Because the shaft is smaller in dia, the window kicks up/down slightly when you wind it down/up, but it sits straight at the top and bottom, and the kick is only minimal anyway.
It's a bit of a 'dirty' fix, but it was at least 6years ago, cost nothing and it hasn't missed a beat since then...
