Here is my update:
Weather is cooler and heat is on all the time in the morning on the way to work. I am experiencing the hot air blasts -- even when moving steady. Not just after sitting at a light. The system then overcompensates with cool air and higher fan speed. It seems to need the pump in conjunction with the monovalve to keep the heater core temp happy.
On a side note, my AC seems to have grenaded. It stalled the car at idle trying to engage, and now makes a horrendous noise. I keep it on EC until I can get it looked at.
1986 300E Anthracite + ECodes + MB Mileage Award