I may end up doing that, but from what I can see, the zip ties I installed a couple of years ago seem to be holding very securely - when I raise the window, there's not visible "rocking" or any sign of extra movement where the zip ties are securing the regulator cables to the window. But I will definitely take a close look for any sign of binding anywhere else. I imagine that will involve removing the regulator, removing the motor, re-installing the regulator, re-attaching the window to the regulator, and then seeing how easily I can move the window up by hand. Hopefully I will be able to judge whether it is binding anywhere.

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2003 X5 4.4i
1992 Porsche 968
2007 328i
2014 Subaru Forester XT