FYI. A couple of months ago my curtain motor started slipping again. I had already taped up the crumbling plastic housing with duct tape. I read somewhere on this website that it was possible to remove the mechanism altogether and then move the curtain on its runners by a rod,attached to the end by the door.
After removing the curtain, I unscrewed the ends,unscrewed the motor after disconnecting the wiring from the switch ,cut the continuous loop drive tape and pulled it all out. The motor housing crumbled in my hands !! I reinstalled the end caps,put the curtain back up ,correctly spaced on its runners eh voila !!
In a simple swish I can open and close the whole curtain in seconds......with no worries it is going to stop half way !!