I used to rebuild hoppers - they were usually so gross that I'd scrub the plastic parts with hand cleaner. I make sure only clean, dry quarters go in our hoppers, and even when I have to go in and replace a motor they aren't all that dirty.
It always amazed me when people would send in hoppers for repair and would complain about all the trouble they have with them. These same people would admit that they dump the
coins straight from the bay vaults and vacs into the
changer, rust, bugs, water and all.