This is all quite interesting, and funny at the same time. I've been under the impression for 15 years that all 140s had bulletproof/thick glass. It's the first time I learned otherwise !!
Well, they are thick and unless someone has actually seen "bulletproof" glass it would be very easy to think that they were. What they actually are is simply double pane for quiet and fog resistance. There is dehumidified air between the glass layers. It also brilliantly enabled a strategy for aerodynamic flush mounting, as the inner layer is a slightly larger area than the outer layer and that is the portion rides up and down in the track leaving the outer pane in relief to run up nearly flush with the door frame. The photo in Dave's post up above clearly shows what I'm talking about.
Mechanically elegant, and IMO absolutely brilliant, its main drawbacks being weight and cost, which come to think of it is just like the 140. Another drawback of the design is that they lend themselves to misadjustment, and actually usually left the factory that way. They are actually supposed to be restrained in the upward direction by a mechanical limit stop on the window regulator, and are only supposed to just touch the upper seal channel without pressure. These upper limit stops were, and are never adjusted at all, or adjusted to act far too late in the upward travel. The upper outer door frame surrounding the glass is actually just a complex shape of sheet metal that is there to retain the seal, surround the glass, and nothing more. This misadjustment is the reason just about every 140 sedan you look at look at will have the upper door frame/window surround trim deformed and being pressed off of the door, and why the windows will almost always bounce down out of the channel on one touch closing.
Absolutely infuriating, thanks to factory assemblers, and most servicing technicians the world over. This condition is repairable if the frames haven't been pushed so far off that they are being damaged by contact with the adjacent doors and / or what ever else, but it's a time-consuming PITA and discredited what was actually a fabulous design concept.
The subsequent S-Classes also have double pane glass, but in this case it is simply laminated like a windshield and retained conventionally, so it catches no one's attention, and doesn't get called "bulletproof". The reason for the change was stated to be "weight and cost rationalization"...
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