I have found this site to be a wealth of information.......Matts Classic Cameras: Rangefinders and Compacts.
He's a super guy and the links Matt provides give all sorts of cool info. Just rebuilt the lenses on a 120 Baldalux & 120 Baldix. You have to get a certain mind set, at least I do, when I switch from my usual Nikon SLR's to a folder. Great fun. Very Zen.