Usually when they don't 'park' back at the bottom, it's a bad relay. Does the intermittent function work? If not, that's the culprit.
It's at the top of the driver's fuse panel, conveniently hidden behind a metal support. The relay is a grey rectangular one with 3 vertical blades along the top and 2 horizontal ones beneath...part number in Standard is RY612 and will run you about $20.
When mine failed, I could hear the click when the intermittent function was on, but it wouldn't work.