While it's pretty clear to me that heavy cleaning and refinishing of an original Kentucky (unless the piece is a real train wreck and subject to major restoration) can dramatically reduce the value, how much "cleaning" is acceptable? I'm not talking about taking sandpaper to the metal and wood but, for example, gently clearing away built-up dry oil or obvious encrusted dirt on the brass or on the wood obscuring an original finish. As I see it, dirt is one thing but the patina of centuries of wear is of course quite another. Any thoughts?