I just had a bunch of fun replacing the passenger side rear regulator assembly on my 1991 300D. To date, this is the only time I have found a part to be under-engineered in my car, and I have to say that I'm disappointed in Mercedes for it.

BOTH of my rear windows broke within a week. I scoured the yards and found a few replacement regulators, most of which were broken. Found a good one from an '86 300E for the right rear but when I got it home I found it was not quite the same as my '91. The angle the regulator mounts to the door is different, as is the angle that the motor mounts to the regulator assembly. I made it fit, but it wasn't pretty. Had to drill some new holes in the door and "clearance" the ashtray bezel on the inside. No visible difference once it was reassembled though.

The reason for both failures was the plastic block which controls the ends of the cables. When the window hits the stops there is a lot of force applied to the block and it simply breaks. The part cannot be removed from the regulator assembly and the dealer only sells the whole assembly with motor for nearly $400. Why Mercedes did not cast that block out of metal I will never understand! The front doors on my car as well as all of the older models that I have come into contact with all have the more standard geared-bar type regulators that seem to be more reliable.

I'm sure many of you are already aware of this and maybe there is a known solution - my research in the archives did not turn up much.

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-Dave