If you bought a 50 year old car you would have a mechanic check it over before expecting it to work properly. It never ceases to amaze me that people buy old cameras (by their nature precision instruments) and then spend money on film and processing before wondering why the images aren't quite right. Here in Australia I charge about $130 to completely check a Bolex including the lens collimation, so that a filmmaker can be confident in the equipment and focus on the job at hand - making a film. Sometimes it's a simple thing like a bent side-rail spring or gummed-up gate that can ruin the footage, while the rest of the camera is fine. Sometimes a $30 part needs replacing, or a lens needs a 15 minute adjustment. Other times the camera is a wreck and needs a complete overhaul. But at least you know. Ideally a cine camera should be serviced every few years, even if it seems to keep chugging along. Much like a car. For a complete Bolex service (CLA) I charge about $400.
If you've already spent money on an old camera and want to use it I would urge anyone to first have it checked by a qualified technician. For a few extra dollars you can be confident that the camera will actually function properly.