Christan.
I don't think you will like my answer! The felt rings cover bearings (2 of them) which are on the 'bell crank', at the end of the aileron push rods. Getting to these does mean cutting a hole in to the wing.
To give you an idea - see the attached photo of my ASW15(a). There was a re-enforced wooden ring bonded into the wing at this point, I suspect by the Schleicher factory during manufacture.
If you are having a problem with stiff aileron control , then I found the nylon bushes that the aileron push rod is guided through was the cause of the problem. The rush rods were removed, cleaned and sprayed with Teflon.
I hope that helps. If you want more photos let me know.
