How is Franco Belge glass held in position?

My Mother's Franco Belge stove has the 1" wide strips of glass. Three of them are loose to the point they are almost falling out. I looked very closely at this. It appears to me that they were held in place with a thin bed of high temperature stove cement. (I expected to see some type of rope gasket.) To hold these three pieces of glass in position, could I fill the gap with new high temp stove cement? Or is there some other material that is better. The remainder of the glass is in good condition so I'll only be doing the three panes.

My mother is 76 and lives in the country west of Allentown, PA. She hasn't burned the stove for about ten years but she did leave it connected 'just in case'. As luck would have it, Hurricane Sandy knocked off her power for 60 hours. She started the stove, the house was warm, we were happy! Nothing beats coal!

They were held in place with a flat asbestos gasket. Whatever you use it can not be hard because the glass has to be free to expand and contract. you could use thin flat fiberglass gasket material.