Amen...I've luckily got 5-holes on my 190E, but I've got 15-holes on the 560sl and they're hell to take care of! Not to mention that I've found both Benzes to produce an INSANE amount of dust, the previous owner of the 560sl didn't take very good care of it, so my wheels were charcoal and the actual faces of the wheels are discolored and streaky. (I may have to post pics up later).
Usually I just use two fingers in a washmitt and scrub each hole with my finger tips, but about halfway through each wheel my fingers tend to cramp....gar!
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Anyways, you definitely deserve a pat on the back for the excellent job on that stretch Benz. ...she's certainly a beaut. :goodjob