OK, performed the test described above. The idler arm does ride up/down slightly. Not a lot at all, but slightly. I have the parts, so I'll rebuild it this weekend. I'm also putting new tie rods, intermediate rod, and steering stabilizer on.

Back to that strut for a moment though. sbourg said in an earlier post that "Noise more likely from ball joint or strut problem", and I do suspect that something happened over on that side (new strut mount on that side only, rub mark on the strut body that side only, noise coming from that area only..), so I wonder:

The ball joint is solid as a rock. I got to thinking...If the PO had someone work on that side, say to replace the ball joint, and they didn't properly jack or block up under the lower spring seat, could that have bent the strut and/or tore the strut mount on that side ?

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Andy_M
'98 W140 S320 Black/Black
'06 W164 ML500 AMG White/Grey
'03 Porsche 986 Midnight Blue/Grey