I bought a Contessa Nettel 3 1/4x 4 1/4. At first sight it seemed in pretty rough shape, but I have done a lot of cleaning on it and found it to be a whole lot better than I thought. The Zeiss Ikon shutter is working perfectly and I took the lens glass out separately. They came out spic and span (Nostar 13.5 cm).
So the bellows checked out good, no pin holes or light leaks of any kind. No flaking on the outside, but it did have some white type fungus on it which I cleaned off with alcohol. Then it occurred to me that this is old enough it seems to be actual leather. Leather is after all skin and alcohol dries skin out. Would it be a good idea to put some leather oil (or boot oil) on the bellows (lightly) or for that matter, hand lotion, aloe something like that to keep them from getting brittle?