RE: Electric Step Motor for DP
Take it to an auto parts store. Some of those motors are power window motors for Ford products and are cheaper bought as such.
RE: What stops the step motor?
You have a stripped gear. I had the same problem and was able to extend the life about a year by taking the large aluminum gear off of the shaft and rotating it 180 degrees to get good teeth to contact.
You can not buy replacement gears or the gear assembly. You have to buy an assembly that includes the gears and a new motor and it is about $315.00.