Recycling old electronics is much like trying to win the lottery. Sometimes you win, but often you don't.

If I'm building something I use new where I can. If I do use a recycled part I test it with every method I have at my disposal (which after +40y in the industry I have quite a few, and is way more than just a multi-meter.)

Restoring old gear is a different matter. You replace everything that is broken or dodgy. Sadly some items can defeat you such as the circa 1950's rack mount tube based military grade shortwave radio receiver I picked up in the late '90's, which sits gathering cobwebs due power supply complications, and a major lack of time. I took it on thinking it would be an easy fix but tinkering by previous "tech's" has elevated the difficulty level to stratospheric levels, which is a shame as it is truly a fine work of electro/mechanical art as a device ...