My S8 has the same symptoms, play in steering and clunk when going over bumps. And its just had a new front suspension and all the suspension arms checked professionally so its not those.
I was searching on quattroworld for answers and they suggest adjusting this, as per ElsaWin original procedure.
Worth a try as its a free fix.
Elsawin:
Adjusting power-assisted steering box
Adjusting power-assisted steering box
Two mechanics are required to perform adjustment. Adjust with engine switched off.
‒ Lift vehicle on lifting platform.
‒ Wheels in straight-ahead position.
‒ By turning the steering wheel back and forth (about 30°around centre axle) a rattling noise will be heard if there is excessive steering play.
‒ → The second mechanic should carefully turn the adjustment screw (arrow) until the rattling noise can no longer be heard inside the vehicle.
‒ Carry out a test drive.
‒ Ensure that when manoeuvring or negotiating corners the steering automatically returns smoothly to the straight-ahead position. Adjust setting if necessary.
