You know, when grease and oil dries out it gets really sticky! I figure that if I can remove most of the contaminants, the rest will eventually dry out and burn off.
I also don't see much use for the rear brake since it does only about 30% of the work. I guess for touring or sidecar duty, a powerful rear brake would come in handy, but for solo use, a disc is over-kill. The drum brakes have always been plenty for me.
I've cleaned up brake pads and shoes several times in the past and they worked fine afterwards. Don't recall what I used, may have been carb cleaner or laundry soap. Maybe Lacquer thinner. But afterwards they were light colored after a little sanding.