Some decades back when there was still a lot of equipment using vacuum tubes (valves) a common phrase heard in tech chat was "solid state`. We were aware of a phenomenon related to "SS" that we called "infant mortality", meaning that if a SS device were going to fail it would happen soon after it was put into service. The perception was that if it survived the "infant" period, it would last forever. A perception likely resulting from the reality that the vacuum tube started dying the moment you put it into sevice, and would certainly fail after a few hours of service, 'few' being relative to the life expected from these 'new fangled' SS things. Truth is, SS devices do not last forever, and as you said, internal weakness may be one of the causes. Having a lot of our equipment connected to impulse collectors (antennae) may also play havoc. In some cases it could be technician oops'es.
> I finally got it all together...now I can't remember where I put it<
Sierra Vista, AZ