Yes - PiO will all eventually leak and be a right bloody mess inside your chassis (never buy NOS). They leak slowly and still work (everything just gets a bit greasy). I'd rather use an electrolytic in the signal path than a PiO. Pure snake oil.
I remember some years ago (15 years) when I started to work/service/restore Tube amps, Tube gear and vintage microphones, that many people advised to replace all old PIO caps for new film capacitors, in case there was any PIO in that specific old gear. The reasons were that:
- they didn't age well and are known to deteriorate over time, making them unreliable
- you couldn't depend on then and they can fail in a few different ways
- the dielectric can break down over time
- they can also leak, and once the oil leaks out of them they're useless
- could have corrosion around the edges and pins
- the paper can absorve humidity leading to breakdown
Probably some other reasons, I don't remember all.
But I did as the more experienced people advised, so I always replaced them in old equipment.
It was a surprise to me that in the last years a PIO Hype grew and people started to buy NOS PIO (NOS = OLD) caps to use them in their equipment. It seems they are now popular again for guitars, microphones and other gear.
I don't know if it's just hype and Snake oil or if they really sound better/different,
but I find it really funny that old caps once considered unreliable are now considered the holy grail for some duties.