Vintage flagship japanese amps, late 70's early 80's, some questions...

Greetings to all music lovers out there.

Recently I started have interest in vintage amps, especially from late 70's and early 80's, I noticed that some high end gears from this era, from Luxman, Yamaha, Sansui, have a impressive built quality, the construction of the top of the line gears appears to be made to last a life time, for example: the integrated Sansui AU2000, Yamaha Centennial Series, Denon POA-8000 monoblocks...

I appreciate very much if enthusiasts of this types of gears can clarify some questions that I have:

For what I know, (maybe I'm wrong about this, i don't know) even considering this gears in impressive Near Mint condition, they still will need to be refurbished right? because 40 years old is too much for some internal components keep their optimum quality?

What are the situations that unfortunately, it will be impossible to make this equipments deliver their optimum performance? (remember that just Near Mint equipments are considered)

Anyone had the surprise of equipments from this era surpass the sound quality of modern gears, that you could not imagine that this would happen?

I know this question can falls down to subjective taste, and other objectives like recreate a sound experience from this era, enjoy the nostalgia of vintage equipments and etc...

but what about really be surprised by the quality of a 40 years old equipments don't loose in anything for the modern standards?

Thanks, all additional info that you can add about this subject are very much appreciated, best regards.