Practice for other meters! My backup PR-1 light meter had a hesitating needle and a sticking button. I took it apart and lubed the meter mechanism with Radio Shack Contact/Control Cleaner and Lubricant. Also cleaned the photocell with Windex and re-set the button spring. Now it's dead on with my other one! Simple elegant design, hardy and useful meter.
GAF Memo 35EE. Leaking battery damaged the CdS photocell, discovered when after cleaning the battery chamber the meter would only read the highest setting. Luckily Radio Shack sells little variety packs of photocells! Difference in sensitivity required adjustment of variable resistor. Now it's one of my favorite sharpshooters.
Konica C35 Automatic. Corroded ground wire resulted in inoperative meter though shutter fired enough to take pictures wide open. Symptom: meter needle sits at 2.8, wiggles slightly, shutter fires. Required disassembly and replacement of ground wire from battery chamber to electric eye. Good as new!
Konica Autoreflex T. Took it down to the bones for a shutter problem that turned out to be nothing more than a little spring under the bottom cap that was off its post. (Doh!) While I had it apart I cleaned all the viewfinder glass, the prism and fresnel, and played with the two accessible variable resistors to try and overcome what appears to be a two-stop overvalue in the meter system.
Ikoflex 1C. Fungus on taking lens. Cleaning the fungus off was much easier than taking apart the lens elements - seems like these old Zeiss Ikon cameras required proprietary tools to take apart...makes them tricky to work on even if the problem is relatively simple. Cold cream cleans fungus, Windex cleans cold cream.
Canonet QL19. Stuck shutter. This was round one, when I thought replacing the battery wire would help but it didn't; I cleaned the glass and checked everything out while I was in there. Instead it turned out to be the classic Canonet stuck shutter syndrome (the blades eventually stick together and require solvent to free them). Fixed after many Q-tips dipped in Rosonol lighter fluid, many many shutter clicks in front of the TV.
Contaflex II. Sticky shutter. Complicated and frustrating enough that I had to leave it and come back to it several times. The manual was almost as confusing as it was helpful. Yes I learned a lot. One thing I learned was that I don't like working on this camera. No wonder CLA estimates are so high for this one. Stressful enough to require a cold one to calm my nerves.
Argus C4. Rangefinder/focus problems. I got the rangefinder working smoothly again and tightened the connection between the slipping gears, which turned out to be easier than I thought. It's reattatching the lens that's tricky!