It would take too long to describe all the ways electronics degrade over time and conditions, so for those with time, it's covered nicely here
https://en.wikipedia.org/wiki/Failur...nic_components Working in component manufacturing for a variety of electronics companies, some parts fail before others, some burn in procedures were to eliminate unreliable components, that today are now reduced to far fewer components on a PCB made in China that who knows what priority the put on PDA? Personally I'd stop using a radio after 10 years considering what the cost of a better ( feature packed ) new one costs and what I've invested that goes in the air. The downside, is learning a completely different programming layout and the the time to find what I need to make it do.
How things were made 20-30 years ago are nothing like today's technology. The article is excellent in giving you all the details.