Sponsored Links (Register now to hide all advertisements)
When radio repairmen rejuvenate old radio sets, the first thing they do is replace all the capacitors. They were not made to last due to the materials used back in the day. Mica was the only insulator that had any longevity so it depends on whether they were made with mica or not. Even those didn't last forever.
Modern condensers would use Mylar as a quality insulator if they were built well.