You might want to remove the window and make sure that the metal channel in which the glass is mounted at the bottom is not catching on the arms of the hoisting "X" mechanism. That happened in mine--twice.

Pull the window out and measure the channel width. Should be about the same all along its length, with nothing sticking out (mine rusted out and splayed...I repaired with epoxy and carbon fiber and then had to trim that down to avoid the catching problem.)

Good luck!

John Bonds, '82 240D, 4sp daily driver
Charleston SC