Xantia Rear opening windows

[wrinklet1]

Hi all, and Happy New Year.
I have a '93 Xantia SX TD, and the problem is that the rear electric windows work ok, but the glass comes out of the clip that holds the window glass to the running channel. The glass comes down slowly and goes up slowly on one side on the other the glass detaches from the clip.
Any Idea's???
Paul