Thank you. You are amazing

Seem to remember that there was a plate on the controllers with the last rectifier reading, so as to keep tabs on the control voltage.

As those old rectifiers go bad the DC voltage drops and they start passing more AC that causes a bucking effect on your coils making it harder and harder for them to pick. On newer solid state controllers you will see it lock up or cause all inputs / outputs to fire. I learner a long time ago to take voltage readings AC and DC and write them down. So you may read 120VDC with 2VAC. Then when you start getting weird problems you have a base line to start from. But rectifiers and power supplies will drive you crazey till you get ahead of them and know what they read when everything was normal. Good Luck

if you ever need parts for these old Otis units try Master Elevator Components, they have a lot of parts for the 1950's and before.
www.masterelevator.net

I had a similar issue a few years back and it ended up being a bad interpole on motor. Maybe start checking your loop circuit.