On occasion I've used white distilled vinegar (5% solution) and ran it in the cooling system for two to three days to flush. Afterwards, I used plain tap water to flush the vinegar out then replaced using Amsoil coolant and distilled water (50/50 mix).

I'm still thinking of going with Evans waterless coolant due to the continuous corrosion (rust rust and more rust) I keep finding in the system. Let's face reality here people, water in your cooling system generates rust. That MB engine block isn't cheap, either. I'm ready to end the rust train.......