Rolling window down pulls the seal with it.
 

Guess it's time to replace the seal no? 101 Projects don't cover this one but does anybody have experience with it? Is it difficult and do you have to take the window out?
Thanks.

That usually means it's time to replace it. You might be able to buy some time by lubricating the seal w/ something dry like parrafin and/ or keeping the seal up w/ some contact adhesive.

I've done it a couple of times. You don't have to remove the window but you'll have to take the door panel off. (at least I did)

It's a fairly easy seal to change. Once the old seal is out, you can feed the new seal into the channel. With the door panel off, you can pull the seal into place.