I have a curious problem with my passenger's door power window. The driver's side works fine, so it's nothing to lose sleep over. When I hold the button to roll it down, it slowly wanders to about 2/3 the way down then stops. A light tap at the top of the glass and it winds itself the rest of the way down. Goes up all in one motion with no assistance needed albeit very slow, slower as compared to the driver's window. What you think could be the hold up? The motor works as can be seen. Just maybe grime on the regulator and gears?