I am having the same left front, right rear window problem you had. I also checked the fuse box and saw nothing wrong. I even switched the fuses around between the working pair of windows and the non-working pair, and I still had the same problem. I then triple-checked by trying a spare fuse, but the windows still did not work. You mentioned a "bad" connection in the fuse box, what did you mean by that?

The windows worked yesterday in the morning when I parked the car at work, but they were kaput when I tried to open them for my drive home.

Thanks,
Dan
1985 300D