[Stepper86]

If it´s just the felt that is the problem you can pull the window apart and replace it. Mine was dried out and came out in pieces everytime I opened the window. I found a rubber U-chanel at the local glass shop. It´s sold per feet, so you just buy what you think you need and cut it to the right lenght.I also bought a lenght of J-shaped rubber for the "scraper" at the top and bottom of the window, this one was a litle thin so it did not hold on that well when placed in the aluminium frame, but a little rubber sealant on the side of it fixed that problem.

The only thing I regret not doing was to replace the window seal itself, I reused the old one because it was not torn or broken, but it was a PITA to install. I stuck the window in a drying cabin for an hour and heated it up to get the seal to soften up. It made things easyer, but a new seal would have been much better.
With a new chrome lockstrip installed it looks quite good.
Here are some pictures (sorry for the bad quality) of what I did.