When i bought my 86 300E,the pass window wudnt go up or down. I bought new switches for the console and it still wouldnt work.Took the panel off and pulled the motor out.cleaned it and found out someone had been in their and had tightened the backlash screw on the shaft end. Loosened it a 1/4 turn and reconeccted it to the door and it worked.Also discovered that someone had put a left switch in the right position.