Can someone tell me what the purpose of this part is inside the heater box. There are two of them. They are made of fairly stiff rubber. The part of it you see exposed behind where the heater core goes is the smaller part of it. The larger part is hidden in the cold air passageway behind the heater core housing. My guess is that they helps control the airflow through the cold air passageway or maybe is some sort of damper between the heater core housing and the outside of the heater box.
The reason I am asking is that I destroyed one of these while cleaning my heater box. I don't see these in any of the catalogs and assume they are unavailable. I am going to make something similar to replace it and it would help if I knew what it was supposed to do.
( I hope Paulmanta doesn't mind me using the picture of his heater box for this )