For being 39 years old, this amp is nearly spotless inside. I’d venture to say it may have been opened once before I inspected it myself. Keep in mind that this thing was on the way to the trash compactor (when it had space), my friend found it before that point and grabbed it. Every single pot and switch/button are all ALPS and there are high quality components throughout, including the construction, mating the chassis/heat sinks to the printed circuit boards (PCBs) components.
It is truly an impressive piece of engineering hardware to look at, with the dual transformers and huge internal heat sinks + huge 12,000uF/63V Nichicon power filtering capacitors. The lines and the curves reminds me of a vintage muscle car. After doing a close inspection the only faults I could find were a few of the smaller electrolytics seen in the first post on this Sansui AU-517 (go to previous at the bottom of this page) seemed to have corroded at their bases touching the PCB. Replacing these is a must, but it might work right out of the gate which would be shocking to me.
Now, most capacitors are said to have a lifespan of about 20 years, but this is not universal and many capacitors can last the better part of a century and still work, namely ceramic capacitors.