Robtl.
Have you replace the rubber stoppers on the boom stop plates?
I had a similar problem today and thought the boom was binding up. I replaced the rubber stops and then the proxes. Mine would always stop at the back of the car. The red lion would have an error that the boom motor ran too long. The motor was not hot and we had not been that busy yet. It might run a couple of cars but would fault out after it had soaked them in
soap. I finallly found a niche in the communcations cable where in comes out of the box to the bay. It had found a spot between the spiral wrap and was shorting out when the boom was extended to the back.
PS I had never even noticed the rubber stoppers were missing until I had this problem.
I have also found out that on the inverter drives that you need a fuse kit between them that will keep a short from taking out ALL 3 of the drives in the gantry electrical cabinet. I ordered the kit from Coleman because I just found out about it.