On certain vintage decks (15+ years old), you also need to watch out for the brown or yellow glue situation. It's an adhesive used to physically mount components that may otherwise fatigue the mounting leads/solder attachment because of vibration in shipping or mobile use. The glue becomes acidic and conductive over time, which can really spice up your troubleshooting/benchwork. More info from one of many electronics forums that have discussed it:
https://www.eevblog.com/forum/projec...lue-easily/25/
I'm willing to bet it's been discussed here and on AK as well...