You would be wise to CLA the body, lenses and backs. 20 years is a long time to sit. Lubricants get stiff, light seals dry out, everything gets hard to work, and forcing dry parts to work leads to wear or other problems. If it is a 500 C, it's going to be 30+ years old, and may never have been serviced since it left the factory. It probably has an original viewing screen, which is not very bright compared to the Acute-Matte screens. Get the CLA done once, and you will be set for a decade. Use a camera that is out of adjustment, and you might have problems. Trust me on this - I found out the hard (expensive) way.

Peter Gomena