I ordered 6 meters to be sure, I cut a little off where I ripped it pulling it through, and that went from the very top all the way round and underneath. the photos I have are crap. But if it dry the morrow I,ll take some more. The channels still bedding in, Aye the windows where still fitted. it just takes a wee bit of moving the windows back and forth. doing this allows the seal to be pulled along. I then held it in place and moved the window back. I kept doing this until I could grasp some of the seal with needle tip pliers and pulled it through. It don't take long, if you still have the plastic runners in the bottom leave them in.
Are you sure the draught isn,t coming through the vertical seal between the 2 planes?...think that's one of my issues, replacement parts are around 40 quid for all the parts but you have to drill out all the rivits to split the frame to change.(summer job me thinks)