Rear Window Breakage
In case you have had no incidents like hitting it with sharp objects etc, I would bring this theory (hypothesis?) to the dealer, ask for their opinion and possibly indicate a due warranty claim.

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However, in the case of CA Bob, I would expect finding fragments of the window inside if such a tool had been used from the outside, not at least bearing in mind the tilting (angle) of the rear window.
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I have destroyed hundreds of windows that way when I used to part time at a salvage yard.
The simplest explanation is often the closest to the truth. Your window was broken because somebody wanted it broken. With the bad economy there are a lot of Mercedes haters out there.






