I just finished repairing my front power windows on my 1980 300SD, and I had searched before I ever tackled these and found some conflicting information about the best way to get these blasted regulators and motors out. The factory manual has some info, but not enough to get you started. If you find yourself with a window that won't work, the first thing to do is to take the door panel off (about 5 minutes to get all the little trim pieces off and wiggle the thing off) and observe the two meshing gears that you can see once the door panel is removed. It will be obvious if the motor is trying to move it (motor is probably, although not necessarily, good if the gear that is towards the front of the car moves). If this gear moves, and the other one just ratchets then your regulator is bad. There are two approaches to pulling the regulator/motor out and I used both on my car. My passenger's side front door had a bad motor, so I took the approach of pulling the regulator/motor out as a unit. It will not come out as a unit past the window guide rail as the motor will "hang up" on the rail. Here's what you need to do first. You will need to get the window part of the way down if you can, and reach behind the regulator "arm" and there is a clip that must be pulled off and a nylon washer behind it. This will free the regulator arm from the horizontal track at the bottom of the glass. Next step is to remove the two screws on the wire junction block at the bottom of the regulator. Once done, you will notice there are two sets of wires, two green and two black, and they are all encased in a loose piece of plastic tubing. There is also a zip tie just inside the door shell that secures these wires that needs to be cut to free the wires up.. You need to pull the tubing off, and it will leave you with a set of wires (one green, one black) that is further sheathed as a cord (this comes from the center console switch, and is essentially part of the door) and the other set is loose and comes from the motor. At this point, you will need to concentrate on removing the window guide rail that is in the forward part of the door. Go up to the mirror adjuster, and you will see a little serrated piece that is part of the black "knob" on the adjusting arm. Take a screwdriver and delicately slide this piece out, towards the mirror. This secures the plastic "knob" on the adjusting arm, and once moved will allow you to tap the plastic knob off of the arm, tapping it REARWARD toward the back of the car. You will then find a small phillips screw on the silver triangular trim piece that surrounds the mirror adjuster, remove it and remove the trim piece. You will find two larger bolts now exposed (10mm head), remove them and also remove the three phillips head screws that secure the mirror to the door and delicately take the mirror off. Now comes the tricky part. Now that your regulator arm has been freed from the horizontal track of the glass, you can rock your glass COUNTERCLOCKWISE and move it out of engagement with the forward track of the window guide rail you are trying to remove. Do this and also carefully remove the channel seal in the window guide rail starting down in the body of the door up to about 2 inches above where the mirror was. You will also need to pop both the inner and outer seal pieces that seal against and wipe the glass horizontally - both just pry straight up. Now go back to the guide rail/mirror mount, you will see some foam rubber at the very top of this piece now that the u-shaped rubber/felt is pulled out. Peel it back very carefully at the bottom of where the foam rubber starts and you will find one single phillips head screw that secures the top of the guide rail/mirror mount to the door frame. Remove this and the rail can be moved horizontally enough to pull it up and out of the body. All this sounds complicated, but I got to this point in a matter of minutes. You can now take the (2) 10mm headed bolts and (1) 10mm nut off of the regulator and take the unit out as a whole and put your replacement back in reversing the above steps. You may find, as I did on my drivers side, that the motor is good but the regulator is slipping due to warpage or cracks or stripped gears. There is a procedure for taking the regulator off without removing the motor from the door frame. This is handy as it saves all the work removing the window channel. You may already have three holes in the door exposing the three allen head screws that secure the motor to the regulator, or you may have to drill these holes. There is a template on the w116.org site - here's the link

http://handbook.w116.org/Chassis%5C72-183.pdf

You will need a 20mm or 7/8" holesaw to do these holes if you have to cut them. Once you have access to the screws, you remove the three screws and take the retaining clip and nylon washer off of the back of the regulator arm and the regulator can be wiggled out (you do still have to take the wires loose from the terminal block, but you don't have to separate them or even remove the zip tie as they will be staying in the door along with the motor. Wiggle the new (or less damaged) regulator in place and play "find the three holes blind" game to get the motor back attached and test it out. I would have shot some digital pictures, but my camera is out of town with my wife (that's how I ended up with enough time to do this today).