Erich, yes let them be, so long as there is no on going deteriation, such as rust or the green gunk on nickle or brass/copper fittings, then, at least with respect for the piece, stop that. Personally, I like to clean em once, for me, then let em go after that, many collectors would be suprised at how many imperfections will be 'hidden' on an uncleaned piece.
Nolan
