Also, you may have a cracked or broken wire between the chassis and the door. 20 years of opening and closing the doors puts stress on the wiring, bending back and forth. you might consider looking there too.

Windows are powered in a cross pattern. 2 fuses. 1 does front left/ right rear. The other powers Front right/ left rear. So if you have both drivers side windows operating, it isnt a fuse or a relay. Swapping the switches is smart, but note that for the rear, I believe that if the rear switch is bad, power from the front switch will not operate the motor.

Wiring diagrams are available. I'd love to have one for my W124 and W210.

Best of luck.

__________________
85 300D 3 pedal. Current project.
83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.