Maybe the motor isn't getting enough voltage to overpower the friction of the seal when the window is all the way up? Could try cleaning all the contacts on route to the motor and see if it helps. Otherwise, I'd guess the motor's on the way out.

On a related note, is there a way to increase the speed of the windows? I believe upping the voltage to the motors would speed up the winows' travel time, but are they already getting full battery voltage? Hate spending a minite or two to roll up all the windows when I park.
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-Sean, Thinking of calling my car 'Black Lung' for the cigarette burns in the seats, the Marlboro wrappers under the handbrake cover and the nicotine film all over the instrument cluster.