A new paper is out today in Nature discussing ISS results of imaging of the F-ring and the shepard moon Prometheus. Cassini has been investigating how Prometheus eccentric orbit has contributed to the appearance of the strange structures visible within the ring. The ISS press release goes into this interaction and a mosaic has been released showing the "channels" and gores in the F-ring caused by Prometheus.

I wouldn't count out Pandora either... while it may effect the F-ring in a much less severe manner than Prometheus, the thick regolith on that satellite maybe related to infalling material from the F-ring on that satellite IMHO. I can only imagine how thick a mantle Prometheus has