1. MB coolant was tested in the MB engines, the others were not.
2. Yes, there are different alloys used in MB engines than used in those of other cars.
3. Increased corrosion will lead to earlier leaks, like at the water pump shaft. MB water pumps cost several hundred dollars. I would rather leave the old stuff in there than try to save $4.95 with a bottle of Pep Boys' finest.

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Prost!