If you can post up some good quality photos of the control cabinet internals, along with anything that looks like model/part No.s, then I'm sure we'll be able to advise on what's currently fitted, and the possible options for a retrofit.
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While things are working, if you've got time and not already got a wiring diagram, it's probably worth starting to make one. Trace where wires go, and what they do. It means that when the time comes, you've got a head start on wiring in a new controller.