Steering rack clunk at input shaft

[ps2cho]

This is on my 2008 E350 4Matic (123k miles now)

I have a weird suspension/steering clunk that occurs when I drive the car up a curb, and it does it worse when the car is turning at the same time.
I've replaced all control arms, upper and lower ball joints and its still doing it.

I got under the car today and had a helper move the steering wheel back and forth, and I found a clunk at the input shaft to the steering rack.
I have no idea whether this is the same problem, but at least I can start here...

Any ideas what this noise is? Is this wear in the actual rack, or what else could it be?
Here is a video:
https://www.youtube.com/watch?v=uN44-G4g5Tc