To fit the screen:
Make sure the area where the seal locates in the frame is clean and free from bits of old seal, sealant, flaky paint etc:
Fit the windscreen seal to the glass....
...until it is located neatly all the way around:
Then start to feed a length of cord into the groove in the seal which locates in the frame:
Not a very clear photo but he had fed the cord through the nozzle of an old sealant cannister and was using this to feed and locate the cord in the groove:
He left two loops of cord at either side of the screen:
The whole lot then is rested into the screen frame:
The lip of the seal is then gently eased over the lip in the frame by pulling on the cord:
To ensure the screen is not forced sideways out of the frame you need try to pull from both sides at the same time:
Keep easing the lip in, you will probably need to pull quite hard in places - especially at the corners:
The last bit:
Refit the interior frame trim, clean the glass and that's it.
I have used a fairly strong mix of washing up liquid and water to lubricate the seal while refitting and when dry have also injected a bead of sealant under the lip of the seal between the frame and the glass but this chap used no lubricant or sealant. He reused the original seal (it's pretty new anyway) but it's obviously a false economy to refit an old perished seal.