Thank you, Jcyuhn, your advice got me back on track and the heater box is out! I had removed the sides of the box while it was still in the car, the sides that connect to the ducts going to the outer dash vents. Should the entire box have been removed with the sides still attached?

MB used foam around several of the flaps and around the sides of the heater core. On my car that foam is badly deteriorated. Should I blow away the flaking remnants or do I need to take some other remedial action?

I very much appreciate your taking the time to answer my SOS yesterday.

Frank