S-Class rear bump steer problem

[rtaylo47]

01 S55 amg
When going over a bump the rear end shifts laterally even when going straight.
Upon visually inspecting the rear end components only the "control arm link"(has ball joint on one end) seems to be so so.
Unsure about the bushing pressed into the knuckle for lower control arm.

What is the right way to check these components other than a visual look.
No play is notice from grabbing the wheel top and bottom and trying to move it. Done without extra eyes.

What could cause this bump steer?