The rear windows are dropping down. When i pulled the door apart, the square plastic clips that hold the window to the lift are broken. I got replacement clips but they have to be pressed on and are not bolted on. How do I install them?

You have to peen (mushroom) the new sliders onto the arm of the regulator. Proabably easier done with the regulator out of the car but the side intrusion beam in US cars makes that job a PITA.

I don't know why MB didn't make it so you can replace the plastic parts without removing the old aluminum pin.

Sixto
95 S420
87 300SDL

You must remove the regulator from the door.

Then you must use a Dremel to grind away the remnant of the old rivet.

Then you must take the new plastic piece apart prior to putting it in the arm. If you do not take it apart, you will mash it to smitheerens and you will need to buy another one (I know this).

After the plastic piece is apart, you can install it in the arm and carefully peen over the end of the rivet using a small steel plate underneath the head of the rivet. When done peening, reassemble the plastic piece and reinstall the regulator back into the door.