One thing I'm always amazed at is how some of the best cameras can be bought on ebay at great prices simply because few sellers spend just a few minutes cleaning up the cameras they find at garage sales or in the attic before photographing them and listing them.  The metal bodied cameras of the 1930's through 1970s were built like battleships.  They clean up beautifully.  I've collected better than 150 cameras on ebay over the last 2 years and have had great luck in winning high quality equipment that I shoot at least a roll of film with each of them. 

Somebody may consider this a sacriledge, but I clean up each and every one of them using baby wipes.  These things clean up everything from leather to metal and plastic parts.  and I have never seen it damage any camera with whatever chemicals are in the wipe.  Maybe some other brand might do damage, but I can vouch that the Kirkland brand from Costco does no harm and does a great job in taking off everything but corrosion.  Clean lens glass with proper lens cloths, though and use proper lens cleaning fluid (if you must) so you don't take the delicate coating off lenses and mirrors. 

Beyond that, one usually just needs to replace the light seals on most cameras and get the proper batteries and then you have a camera that takes great, razor sharp pictures.  The great news is that there are great sellers on ebay that sell light seal replacement kits and hard to find batteries.  I've bought from each of them on more than one occasion and have been very happy with their products.  I suppose the most common of the no-longer-available batteries is the 625 mercury cell that was commonly used in such popular cameras of the 1960's and 1970's like the Cannon FTb SLR, the Canonet Series of Rangefinder Cameras, The Nikkormat FTn, Nikon F, and the Minolta SRT Series of SLR's.  Sure, there are ways to use hearing aid batteries to replace this no longer available button cel, but I'm a very satisfied user of the Wein Cel  MRB625 that provides the exact 1.35Volt power those cameras (and their meters) were designed to use.  Even though they are the zinc/air type they still last over a year in storage after the tab has been removed.  At about $6 per cel they are worth being able to use these classic cameras at their original specs.