When turning the 518 to the extreme left, the steering wheel doesn't just stop, it will continue to turn and the small gear at the end of the steering column will slip against the larger flat steering gear. It makes a loud "click" noise as the gear teeth pushed the flat gear back slightly then slips against the flat gear teeth. Gear teeth look good on both sides. Turning extreme right is fine and the steering wheel stops.
Could it be the flat gear is slightly deformed on one side? Or is there an adjustment