Hi Electrodrive,
It may be a mechanical fault, looking back at the experience I've had with thistruck in the past it may be the steering ring bearing that is partially seized I've had them seized before I have a workshop manual for this truck I will have look see if anything else comes to mind, I've had steer chains broken tach generator gearboxes worn, steer pots worn out, steer motors falling apart

Regards Titus