Info von mgexp.com, die dem Hinweis von Juan entspricht:
The secret is to use some heat. Either a hair dryer, or a heat gun used with care, to warm the non-vulcanized rubber strip so it will form to the edge of the glass and press neatly into the frame.
Push the glass/seal home, into the frame, making sure the seal sticks out on both sides, and then after it cools trim off the excess with a sharp razor blade.
Once it has cooled, the glass will be "glued" into the frame, so make sure you've also properly installed the little metal guard that goes where the latch catches the window closed.
Before replacing the glass, replace the threaded pivot that goes through the hole at the bottom of the frame (get it in right way around!), as these rust and eventually break off.
Gruß
Stolli