Very good news that normal service is restored!
I suppose one other cause might be the lubrication on the gears/screws that the motor runs the pantographs on. Over time the original lubrication might have coagulated (for want of a better word). From the Alex M. video linked above, they look similar to the Acela door mechanisms, which are a real bore to try to maintain. As my set had lived in a box for some years, I put light oil on the door gears to get them running. This was no easy task; I have never had the nerve to take one of the cars apart although I have had both engines open.
