I think the metal channel and the roller are "one piece" ... you can see by my pics (see link above) that the window comes out, off the regulator, by cocking it. The roller comes out with the window. Then, when you put the window back, you just slide the roller into the regulator channel (if I remember correctly).
It wasn't a problem for me when I did it -- but I didn't replace the glass, I just took the window out to refelt everything. Then I did it all again when I put new vent windows in ... again, it went well.
If your window is binding, it's tilting when going up or down. Mine was binding, too ... but after I put new felts in, which snugged everything up, it wasn't binding anymore.
