[35Z5]

Most issues in any of these radios whether US or Japanese are due to dried out electrolytic capacitors. More there are, higher the odds there will be issues. The A series have five, that's fairly high odds. Later models used less so odds are improved(I believe B, C & E series have only three). The aluminum cased 500 mfd @ 12v used in those was anything but miniature. 

Mostly it boils down to the fact technology to build miniature, low voltage but fairly high value electrolytic caps was still being developed. Early epoxy sealed, ceramic capacitors are very failure prone. Cases split and/or epoxy sealant cracks, allowing air to enter. Somewhere in late '59 IEI/Nashville & Sprague began supplying plastic cased caps that have mostly stood the test of time. The J series wasn't introduced till '63/'64, by then the technology was far more matured(as was cutting corners).