Hope I can be of help.
I just removed the backs of the seats in my 300E, although for a different purpose (needed to replace the cargo nets). The maneuver is not well explained in any of the manuals or the CD.
First remove the two screws at the bottom.
To avoid damage, you should understand that the back of the seat has a V shaped metal groove on either side and that the leather from the sides of the seat folds into this groove very tighty. There are also several metal retaining clips fastened to the edges of the leather.
To force out the folded leather, you need something like a strong but flexible, small putty knife. Beginning at the bottom of each side, carefully lever outward (the fulcrum point being the side of the V rail toward the middle of the seat back) after the putty knife has been inserted in the V deep enough to get a hold on the edge of the leather. After a few attempts, the edge of the leather from the side of the seat will start to pop out, and the whole side can be removed easily after that, using the same technique repeated all the way to the top.
After both sides have been removed, pull out and downward to free the top from two or three clips.
To replace, first slide the top into the clips (may require some hitting with your fist), then reinsert the edges of the side leather deeply into the grooves beginning at the top, and, of course, replace the screws.