I can tell you what the problem is on my wind noise. The frame of the window is bent ever so slightly at the top rear corner, i.e. the window frame is ever so slightly 'sprung' so that it sticks out very slightly proud of the rear window frame, if you know what I mean. (It should be flush across there.) It looks like the PO tried to pry the window frame apart enough to stick a coat hanger or something in there to unlock the door? Who knows.

I diagnosed it by driving the car, opening the rear driver's window, and sticking my left arm out enough to push on the top of the driver's door window frame so as to 'spring' it back into place temporarily. Presto, that instantly stopped the wind noise.

So now I have to fiigure out how to permanently spring the window frame back into place. If I can't do it, it's off to the body shop, that is after I get the motor back together. Maybe check that on yours. I sympathize with your frustration, believe me. By the way I have the same exact car as you, the '93 300E 2.8.