My sons Ford Falcon (with rust ) needed another electric window winder. So again I installed a new one . A week later the winder was slow to work and I was concerned .Turns out he had been with his friends lights on well before starting music brake lights on and his battery was down badly after short runs . I recharged the battery and put silicone on the window frames now all is well slides as it ought . I believe the problems are holding down the button after the window is right down or up straining the mechanism and lubrication of the sliders .As well as bad engineering of the mechanism . Never replaced a Volvo electric unit after 6 Volvo's.