Get a couple gallons of MB coolant and a bottle of the MB citric acid powder cooling system flush agent. Follow the directions thoroughly and refill with 50/50 MB and water. I use only MB coolant in my Mercedes, the BMW, DeLorean and Jensen all get Havoline Extended Life (it's orange too). If you must use the green stuff, I'd say to use the Prestone Low-Tox. We have a few cats around the house and I'm always careful not to spill any coolant or leave any unattended but I always consider switching to Low Tox in my three non MBs.

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Regards,
Aaron