Got the motorhome back. Haven't tried extending and retracting the slide yet but will likely do that when we hit the road in a day or two.
In addition to the cost of the motor and overnight shipping $401, they charged me $462 labor which included a few other things. So while the labor probably more than they needed, overall I'm better off than if I had them get the motor.
They showed me the old motor and it had the same part number 523900 so if anyone says, as my service guy said, they don't make them anymore, just go on line and find one.