Rear window seal REPLACEMENT / Any takers on assistance?

[79300D]

Hey everyone,

I have started the project of replaing the rear window seal on the '78 300D. The old one came off without a hitch, and, the best part is, no rust under the old one. Here's my question:

In putting the new seal on, should I first attach it to the car, or the glass? I know it sounds stupid, but, preliminary tests show that it will not stay on the car during installation, and, if I put it on the window, how do I get it to stay on everywhere else?

Any takers?

Thanks again,

Jeffrey