Vent window gasket

[Voss]

Doing some detailing on my door glass and thought I would fix an annoying gap I have between the top of the vent window gasket and channel. The gasket are in good shape and is an original Mopar piece. Now, the problem I have is to get the gasket nice and tight on the upper end. I can esily stretch it (very very slightly) to get it in the correct place, but it won't stay. I found a tad of some residue I think is sealant or weatherstrip glue. See the picture.

Are these gaskets supposed to be glued on the top? A very small tad of weatherstrip glue would do the job. I'm probably gonna use that but it would be good to know how it should be.