re: Any mechanics on here?

No, nothing professional or of those places. If you know a good radiator shop that's where I would go. Trying to flush it yourself is going to be a big job at this point, you can't rely on the cooling system to flush everything with just using distilled water. It simply won't stir up the sludge that's settled in the radiator, engine block, and heater core. Have to back flush under pressure from a water hose. When I switched to ELC I pulled the radiator and hooked up a garden hose adapter to flush all the old coolant out, refilled with distilled water to flush again, then filled 50/50 ELC and distilled water. Without any additive packs it will last 600k miles at least with a gas engine.