I had the same problem regarding the windows on my '88 300E. As you probably know, the front window and the opposite side rear window are on the same circuit, so check the fuse. I also replaced the console window switches (under $20 each from PartsShop if I remember correctly) but still the front passenger window wouldn't go down. After tracing the wire, the culprit turned out to be the junction block located under the door panel. The wire from the fuse box fastens to one terminal, and the wire going to the window fastens to the other. There was caked residue on the junction block that looked like old grease. I removed the wires, cleaned it off, put a little petroleum jelly on it and then the window worked perfectly.
'88 300E 265K
'91 300TE 155K