So I have taken another look. The window works fine as long as the glass stays on the plastic collar (real oem calls this a "bush"). However, after 10 up/downs the glass has slid almost off the collar and there is nothing keeping the glass on the collar.

My thought was to remove the hex bolt, the collar and the clip. However, the hex bolt won't budge and when I apply some torque to remove it the head starts to strip (I am using an 8 mm open end wrench ... am I using a wrong size?). This also implies that the nut is still in place and that maybe the collar is broken. I think I need to get the bolt out. Am I missing some technique or is it a matter of strength and patience, or something else (I am stuck with my current brain LOL)?

The real oem page is RealOEM.com * BMW E53 X5 3.0i EL.FRONT DOOR WINDOW LIFTING MECHANISM.