This is for John and GreggerT, even though your posts were over a year ago. I had this same problem: "The motors work fine but at each end they fail to stop and click as if a gear in the mechanism is stripped. " You are right, there is a stripped gear, but it's in the scissor lift operator, not in the motor assembly. I took everything completely apart this morning to learn this. There are two large gears in the scissor lift, and a few of the teeth were completely worn away. I haven't found a replacement source yet, but hopefully someone is selling replacement assemblies.
Brian, August 2015