The only camera I have had go wrong was a Pentax K-50 which was my backup so not used much. The aperture solenoid failed well before it was two years old. By the time they eventually replied to me, it was over two years old and out of warranty, they refused to fix it.
They did the same to thousands of other owners, even though it was a known manufacturing fault.
That was the end of my Pentax usage, I had been Pentax since the early 70s
I have often bought faulty cameras on ebay, and I have fully repaired most of them, and the ones I haven't managed are usually the result of just taking a chance.
I think that tell you that if one goes wrong, unless it is valuable, it is uneconomic to have it repaired, but there are lots, so faults can't be that uncommon.
Best thing to do with old cameras is to keep them for a good while before selling, if it ends up in the back of a cupboard never being used, then maybe sell it.