My 300E 5speed has this option and the nylon belt/cable broke that pushes the shade up. The dealer wanted lots of $$$! I had the new belt all ready to be replaced, and one day I decieded, 'What's the big deal, I can figure it out.' So I fixed it
and it works fine!
What most likely happend is that the teeth on the belt are worn and slipping in the motor (my belt snapped) this won't work if the motor is shot...but if that is the case you can do this to lower the shade. So unscrew the rod that attaches to the ceiling, and remove the sunshade from the rod, pull the rod from the belt as the belt is inside the rod. Oh! MAKE SURE you put a towel down as some of the parts are greasy!
Next, get someone (you can try to do it yourself) to push the sunshade up button, while you guide the belt out...you might have to pull a little, but only with the motor running, (notice the direction the teeth go into the hole for the motor, also note that their is an end that is smooth that goes toward the shade of toward the front of the car). You have no removed the belt! Take the new belt and you'll notice it is longer than the old one, don't panic. You have to cut it down. To cut it use a razor blade and score it, once you have it scored snape it off. Next, get back in the car and guide the belt in and have someone push the down sunshade button and viola, the new belt is moving. Next put the sunshade on the rod and then guide a the belt in the rod, push the rod down on the mount near the shade motor and put the bracket for the ceiling back on and secure. Note, on my car (at the time ~163k) the celing bracket was loose, this is from vibration and the holes have loosesd...so use larger screws if this is a problem. Let me know if I wasn't clear. BTW whole job was about 1.5hours for me. Tools: Phillips Screwdriver, razor blade, towels.