Fine Scratches on Driver Side Door Glass

[Zen]

I've started noticing very fine vertical scratches on the outside face of the driver's window of my 4-yr old S4. Winding the window full down and running a finger along the fibrous pad beneath the outer rubber flap, it feels like sandpaper. This pad, which is always in contact with the glass, clearly picks up and accumulates any small grains of debris from the glass when it is wound down. Any ideas on how to clean this?

This is not a new problem: I had the same on my Audi Coupe GT and eventually the glass started to become opaque.

[Tomson]

The only thing I can think of is taking the window down all the way and washing the felt part with soapy warm water