126 Mono/Duovalve again...

[gidpor]

I am slowly progressing with my now ongoing heating saga. Eliminating things as I go along. It has been months now - So again I am asking for guidance from the knowledge source.
Just to recap, I had constant heat in the car (1987 300SE EURO - which is with Manual climate Control- not PBU) , so I first replaced both inserts on the duo-valve. They were bad . That fixed it on an intermittent basis. I next purchased a used valve, put the good inserts into it's "top" and replaced the top of my existing unit with the "new one". Things are different now. If I never use the heat - All is well. If however, when car is running I turn the heat on by rotating the temperature dials and then turn it down again - The heat will not go away.
The temp sensor in the light dome sucks air.
I checked the valve inserts with direct 12v - they click as supposed to.
I checked the electrical connector to the valve with KOEO. I get 12.4v with the dials in the off position. then pulsating with dials in white or red. Finally returning to 12.4v when dials turned down to OFF again. So it seems that the system works correctly with KOEO but somehow does not when the car is running at temperature. Where do you think I should look ? Could the valve be malfunctioning when hot ? Could the dials be at fault Somehow not functioning when they are "hot" ? Or might the problem be elsewhere like a faulty ground. I am at a loss here.
I should mention that I purchased the inserts online and realized they came in a blue box (forgot the make) rather than the Bosch yellow. I do not think that has anything to do with anything but am mentioning this because every detail matters. Any help would be appreciated