I am checking out an old Power Designs Model 2005A which has been sitting in a garage for a long time. I don't have anything to check it with better than a Keithley 196 DMM (from ebay, and 4 years out of calibration). The 2005A seems to mostly work. After warmup, the OVEN lamp flickers sometimes as it probably should, and the indicated voltage output drifts less than 20 ppm in one day. However, pressing on or slightly jiggling any of the four rotary voltage selectors shows some jumpiness in the output, so clearly there are dirty contacts. I haven't taken it apart yet. Are these contacts copper, silver, gold, something else? Is a spray with contact cleaner likely to help, or will a full disassembly and/or replacement be the only cure? I have seen Caig DeoxIT recommended, but they seem to sell many different varieties for different contact metals and situations.
Update: ironically, *as I was writing this post* the Keithley's LED display blinked out (it had been working without issue for months). The internal analog +/- 15V power rails are still ok... anyway, a problem for another post.