My guess is that this subject has been discussed so much that many are sick of it.

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As I recall MB doesn't like 10W30 M1. Since M1 0W40 has been factory fill for at least four years now, at least for the US market, I see no reason not to use it year round, which I do. My C320 is still in warranty but I do a change at the FSS halfway point which ends up being 5-6000 miles. But, M1 15/50 can be bought cheaper (at WalMart, biggest Mobil 1 retailer on the planet) and it's on the MB approved list.

Your plan is fine except for the viscosity.