Either the shutters or the irises can cause differential exposures.  Many of these folding cameras had shutters and irises that were made up from sets of very thin steel blades.  Any oil film can slow these down.  If there is any rust on the blades or the pivots (the pins that hold the blades), this will "trap" any gook that is slowing them down.  This can be seen as a brownish discoloring of the normally black or blue-black blades.  If you use a solvent, make sure that it does not have any water in it.  Some rubbing alcohols are actually a mixture of solvent and water, and this can rust steel blades.  Also, be sure that all of the solvent has evaporated before actuating the blades.   And, be very, very careful not to put any pressure on the blades.  They are very easily bent, and almost impossible to straighten once bent.  The slightest bend will cause them to rub or even jam.  Normally a very thin film of light oil will keep them operating smoothly and prevent rusting in normal temperatures.   They can be operated for short periods of time without any oil in extremely cold temperatures, but they should be re-coated with the protective oil film when returning to normal temperature use.  There is a very light machine oil, called "camera oil" intended for this purpose.  It is sold to camera repair shops.  Some modern synthetic oils will have a wider temperature range than older "natural" oils.  If you are not absolutely sure that you can do a safe CLA (clean, lubricate, adjust) yourself, you may be better to have an experienced camera repair shop do it.  There are several that specialize in older cameras which often have sticky shutters.  They can also check the timing on your shutters, and adjust them if they are off by very much from the labeled speeds.  Be sure to tell them that you plan on cold weather operation, and they will use a lighter oil.  Some will recommend that you use the thinner or lighter weight oil for cold weather operation, and then have a CLA to a normal weight when returning to warm weather, just like with a car.  

JR

That is very interesting about your stereoscopic vision.  You might want to check with an ophthalmologist to see if this can be corrected.  And, check with more than one.   There are some new treatments that some doctors may not be aware of.  Interestingly, some of these treatments and therapy involve eye training and eye muscle exercise using stereoscopic images.  There are people who have had their vision corrected for amblyopia and/or strabismus who told me that they wished that they had these problems corrected long ago; that it opened up a whole new visual world for them that they did not realize existed.