The red arrow points to the defective volume control. So where do you find a replacement for a 40 year old volume control?
You find it in a used donor remote station from the same system model.
This is a great example of how a single small part like a control assembly from a Model 2570 remote station can provide enough parts to repair several other units.
Without a supply of good used parts, this 2561 would still have a bad volume control