Epoxy coated ovals (whether polyester or polypropylene), are wound loose and then squished. Most capacitors are made with film from recycled material, and then wound as tight as possible to keep the ESR low. Micro lesions form in the film, exposing the vaporized metallized layer above. This causes arcing, and while low level, is a source of noise in the signal path. If you can generate enough voltage, the arcing creates heat to soften the damaged film areas, which closes the holes. That's why all metallized types are called "self healing". In audio, we don't normally reach the voltages necessary to take advantage of this feature. Value capacitors also suffer from poor lead terminations (they can't solder them so they are pushed in and a paste is used). So, the leads are eventually exposed to oxygen, moisture, and the effects of mechanical vibration. Well made caps use thick virgin film, with leads that are physically attached using a variety of proprietary methods. These caps just happen to carry fancy names on them. You can get them without the fancy names if you are willing to buy 10,000 at a time (in each value). So no, the caps weren't "worn out", but they were the typical bottom of the barrel crap most manufacturers use.