Prior post is my cleaned-up and no longer "sticky" duovalve. Did a coolant change & flush today plus a properly OCD-worthy job of cleaning all the gunk off the duovalve. It reacts instantly now to me adjusting the temp ****(s) whereas before it responded very sluggishly if at all. Having the duovalve plungers removed helped when back-flashing the cooling system with fresh water. A LOT of old blue coolant came pouring out of the two openings. The coolant is now a very faint yellow without even a hint of green, so I know all the old stuff was eradicated. Anyway success and don't have to shell out for a new valve.