I know the real answer to this question is do not store cameras long term in their cases, but it's so convenient ...........
I have a fairly large collection of Soviet rangefinders going back to pre 1940. The problem is that a small number have small areas of green gunge on the chrome (verdigris?). If left unchecked this attacks the chrome and removes small flakes. It's easy enough to keep to a minimum and can be removed with the universal panacea of naptha.
However, I'm fairly sure that this is not helped by the dirt grime and whatever else has decided to lurk in the linings of the cases over the decades. My initial reaction is to use spray car upholstery cleaner and use a stiff brush to work it well into the lining and then allow the case to dry out slowly. Unless anyone has any other suggestions to consider??
Early Soviet chrome-plating is very poor and I have seen examples damaged by normal handling. Finger prints clearly defined in corrosion products.
Storing in the case is convenient and does give good protection when you store a large number together. Like you I have a fair number of early FED and Zorki models. The ones that are stored in their cases have the chrome top and base plates protected by a strip of cling-film. The film just covers the chrome plates, it is not wrapped round the whole camera. Have done this for a few years and had no 'verdigris' problem.
As for cleaning the case linings; I have used a cloth dampened with a strong solution of ordinary washing powder and done similar with a Ronsonol soaked cloth. The best results were obtain with an aerosol can of 'dry cleaning agent, purchased from the laundry dept of my local supermarket. Look for the product amongst the stain removers. This product seems to be a 'talc' suspension in a non-flam solvent. You spray on and wait for the solvent to evaporate, then brush off the white residue plus dirt/grease. For case interiors I use a large tooth brush to remove the residue.
