under that kind of stress I'd strongly consider running synthetic 20w50..

only .5 bar @ hot idle would make me nervous...I'd pop her into neutral while sitting for any length of time.

Jonathan

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Blue Ridge Mercedes
Jonathan Hodgman
http://www.blueridgemb.com/
Enthusiast Service, Restoration & Tuning.
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Located in the Atlanta area
Specializing in all pre and post merger AMG's including Hammers and DOHC M117 engines.
Mercedes Repair Atlanta