Actually Erno its quite simple and I have done it loads of times.
I'm assuming you have the felt strip CZL000020.
Now, if you put a tie wrap around the window catch to keep it from locking it makes it a whole lot easier. Using a small flat bladed screwdriver you can dig out the old felt from the channel at the leading edge of the window. Now gently slide the window back a little bit and hold onto the felt, now pull the window back towards the front and the felt will come with the window, keep repeating this until the whole of the felt has come out.
Clean the entire upper channel thoroughly.
Now feed the felt into the top of the leading edge of the window gently so that it is caught by the leading edge of the glass, slide the window backwards a few cms and let the felt go with it, push the felt into the channel and then slide the window forwards, keep repeating until the window has taken the correct length of felt with it. push the remainder into the channel and job done
Rob
