What do you folks do to loosen very stuck retaining rings? I have a good spanner wrench but sometimes I must give up trying to loosen the terribly stubborn ones. The one giving me problems now is one of those ultra-thin Copal #00 rings with very tiny slots. I've already marred the back of the lens board and the ring. Things like this frustrate the heck out of me. I do stop before I get really ticked off and mess up the lens... learned that the hard way long ago.