1998 C280 Drivers Window Sticking

[lacombe]

The drivers side window on my wife's C280 would not go up or down, but could hear the motor running when toggling the switch.
Took the door panel off, and found the mechanism with gears on it (is that the regulator) had come completely loose, so I riveted (hope aluminium rivets OK) it back to the door.
After riveting the window would go up and down, but occasionally needing a little encouragement by pulling on the glass, especially when window almost all the way closed.
I noticed the glass is not all the way seated in the U shaped metal rail; I can see clean glass, and can tell it used to sit deeper in the rail.

How does one re-seat the glass in the rail?

Could this cause the window to stick?

Thanks for any suggestions.