On my 1991 300SE, I can make the driver side front window slide up or down by putting my palms on either side of the glass and pushing up or down. Not that I need to do much pushing down … gravity does that gradually, as I drive.
Today, I analyzed a parts donor car, so as to learn more about likely causes of the problem, and how to get access to the relevant parts.
The first step was to open the door. No problem there.
I removed the seat control switches. I pulled the little black plastic miniature-seat pieces away from the door to remove them. Then, I pried away the plastic cover just below that. One side has three fairly flexible tabs, and the other side has one large tab. I broke one of the tabs on one side. With the cover out of the way, two small yellow Phillips screws become visible, and with them removed, the switch base could be accessed and removed. I also pulled the wiring plug away from each switch.
I removed the door handle. With the window switch base out of the way, a large yellow Phillips screw becomes visible. I removed that, and two similar screws in recesses in the door handle. With the three screws removed, the door handle can be lifted free.
I removed the door lock knob, by turning it counter-clockwise and then lifting it away.
I pulled the door trim away from the metal of the door; I own a tool for that but I hadn’t brought it along. Girl arm muscles worked well enough, as did digging in my nails around the edges to pry the panel away.
I removed several (non-identical) 10mm bolts and one or two 10mm nutes, and the window winder mechanism came loose. I chased its wires. Two of them can be loosened by removing two Phillips screws, but there’s another three-wire harness for which I couldn’t find an easy disconnect point, so I cut the wires.
I could maneuver the mechanism downward but not free of the two metal guides at the bottom of the window glass, until I removed a 10mm bolt that was clamping the mechanism to the guide.
I’m not sure that I needed to get the window out, or remove parts in order to get the window out, but I did anyway.
The two vertical guides for the glass are non-detachable as far as I can tell.