I have a cupboard with 3 or 4 dud camera bodies in it. Mostly Nikon & Olympus. Came to the realisation that it was all about the degree of automation in them. Aperture priority was a great technical advance, but while 70's & early 80's manufacturing was pretty good, the electronics just weren't built to last. Then there seemed to be a tipping point in the late 80's and early 90's when they got the electronics nailed down and reliable.
Same thing seems to have occurred with the use of plastics replacing metal parts - worked fine, but never intended to last 30-40+ years (which is where we're at now).
Now, I tend to stick to fully mechanical bodies or late-stage electronic ones; otherwise I just have to accept that bodies from a particular era of manufacturing are going to have a high failure rate.
Good luck in the quest to find something usable.