It does sound like the fixing to the window is at fault I guess you have checked the obvious like ensuring the whole mechanism is fixed and no screws are missing from the assembly. As someone who has carried out the Phines modification (second time on the drivers right hand side) I can say that it does work. What I did the second time was remove the electric motor and run the window up and down by hand this helps find the tight sections of the rail once you have opened it up. Since carrying out this check on one side I have never had a problem with the window.