Strange that the cables broke. I've replaced both rear window units in my 300E, regulator mechanisms were fine but the motors had burned out.

Replaced the front motors shortly after as well, seems like they weren't designed to last the life of the car. I'm told this is a Known Fault with the 124

It may not have been a normal occurrence. On the route I take to and from work daily, there has been continuous road and home construction for the past two years, which generates a lot of airborne dust and dirt.

Because my sunroof and both rear windows failed at the same time, my theory is that every time I opened and closed my windows and sunroof, a tiny bit of that dust and dirt got into the control mechanisms. Multiply that tiny bit by about 1,000 open/close cycles, and mix it with the lubricating grease on the sunroof and window tracks, and you have an effective window/sunroof jammer & killer (if you do not routinely clean and lubricate the sliding parts, which I did not).

Initially, I assumed some plastic parts had broken, and was shocked to see that they were in pristine condition.