I owned an 87 300SDL, which is the diesel version of your car. I eventually replaced 3 of the 4 window regulators...and I thought we used the windows very sparingly.
I think these were the most disappointing failures I had with that car. MB really boned the design of the regulators...I'm sure as a "cost savings".
I had a saab that I beat to heck...15 years and 250kmiles... with power windows, and they always worked. Never had a power window failure.
I love MBs, but not anything newer than 85. Yes...I know..I'm obsolete.