I do not know what a 'rotary drive unit' is. The bit I need is the control unit where you press buttons to set the unit, with Auto/Standby, +- 10, +-1 etc.
Is this what you mean?
I understand that the critical fact is whether or not the unit used Seatalk
and I am told that is know frokm the number of wires it connects to.
Any further info welcome please. If it is the right unit, I would be pleased to buy it.