61 4dr. rear stationary glass sealant?

[61 Waycrosscomet]

As there is no place I can find to replace the rubber around the glass of the 2 back door stationary triangle windows, I am just reusing what is there.
A little cracked but.....
Question: The glass appears loose in the rubber gasket, should it be sealed with something? ie between the glass and rubber OR some sort of
sealant between the rubber and the metal frame it slides into?
Can't see any residue to tell if anything was there.

Finally, I plan to swap the triangle glass and rubber with the other side, so what was outside rubber all these years is now inside and visa versa
hopefully extending life of rubber. No, I don't want to try to remove rubber for fear of it snapping apart.
Thanks for any help and tips. john.m