Coming up on 137K miles, there is a "clunk" sound / felt when quickly depressing the clutch at low speeds. Usually when the engine is braking.

There is also a rumble or slight shake when the engine is idle. The engine runs great however.

So I am thinking it is the Flywheel, but input would be most appreciated.

The build date on the door says 01/04. So January 2004 I assume.

Referring to the Parts Manual for this build date shows part number:
05098905AA

One vague photo and a European parts website cross this into A1120301305

In searching the forum I can only find reference to the Mercedes part number for the 4+4 non-symmetrical flywheel

Can anyone confirm this A1120301305 part number?

I have not taken anything apart yet so I hope the parts manual is correct!
And Yes, I will throw a clutch kit in when I do this, if it is the flywheel.
I don't see anyone describing these symptoms for a throw out bearing or slave cylinder.