This may sound crazy and may not be what you need. But I had a '96 Disco that had this problem. The dealer said I needed to buy a regulator. But I purchased a (I think it is called) sliding jaw hard plastic piece from the Mercedes dealer for my 1981 Mercedes 300SD. It is rectangular, white, and travels along an aluminum track in the regulator which moves the window up and down; they are designed to bust if there is too much tension on the regulator rather than bending the regulator arm. I took the plastic apart and used one side which fit on the Disco roller with a bit of grinding. Surprisingly it worked perfectly and never had a problem with it again. Will look to see if I have a pic. It was the passenger side window, right rear regulator.
Good luck.