Not so different from asking if a 1975 car was a good one.
The 23-channel Midland models you mention were made by a contractor named "Cybernet", located in Japan.
Those models were as good as any 23-channel AM mobiles at the time. And there were a lot of utterly JUNK 23-channel radios sold during the 23-channel boom period.
But just because your 1975 Duster was a reliable daily driver for a year or two means nothing 40-plus years later.
The radios won't need tires, hoses, belts, seals, bushings, gaskets, carpet and seat covers.
The mileage would dictate how long one of these radios might work before the first "age-related" breakdown. A true NIB radio might be good for a year. Or maybe a month. Hard to predict.
A radio that traveled 80,000 miles in a dump truck will be a different story.
But making any radio that old into a daily driver will call for replacement of *ALL* the electrolytic capacitors. Moving parts are a wild card. After you clean the switches and rotary controls, one or more of them may still cut in and out. Another mileage kind of thing to consider. A control or switch that cuts in and out after cleaning will just have to be replaced. Wear and tear has a big influence on the life of moving parts.
The question isn't about whether or not it will need "40-year maintenance". It's about how soon. The higher the mileage, the sooner that will be.
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