ok, I finally pulled the monovalve. There is a slight tear (enough to replace it I guess). I have found ********az has best price on the repair kit (under $40). Upon reinstalling the same monovalve, I've discovered that the heater is working fine and the car NO LONGER OVERHEATS? what the ****? I can leave it in the driveway with the heater off and it will stay at or just below 100*C, hit the throttle and temp will go down another 5-10*. Next step is a citric acid flush (I think the local homebrew supply will give me food-grade citric acid at about $7/lb). Anybody have any insight on why the car stopped overheating?