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I don't think it is coolant, there is a line that is connected it, I think that is the PVC line.
Yes, it is residue oil. I just did a clean up and run for a week, no more residue oil. I think it is normal operation.
The catch can is built in. See the attached picture.
I have a wife's car 2017 GLE350, basically is the same engine but they remove the catch can and no hole going down.
If you empty it at every 60k miles, that will be much more often than needed. Even 100k miles as Randy suggests, would be frequent enough. You won't find more than an ounce or two, maybe three after 100k, in the catch can. But if it bothers you to go that long, check it at every air filter change, when you already have part of the manifold removed.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
