What would be the best aftermarket (Walmart, Napa, etc.) coolant for a high mileage 2006 Forester? I have a new Subaru radiator cap, and the conditioner on hand. I am only interested in draining the rad/coolant bottle. The color of the coolant in the bottle is greenish brown, a mix of used coolant from neglectful owner. This is a charity job, just don't want to make things worse. I have peak Global green in the garage now. Walmart has Zerex asian I think. Thanks in advance all!