What kind of capacitor is this?
Well, it's a polystyrene cap. These used to be one of the best cap types for audio (lowest distortion), however they have been obsoleted for a few  very simple reasons...


Polystyrene can't be metallized, it has to be wound film/foil, which is expensive.
Polystyrene can't be surface mounted because it melts at low temp


MKT/MKP would also melt in SMD. But there is enough market to keep them going. Not so for polystyrene.


For low values where you can get them, C0G/NP0 ceramics are smaller, cheaper, just as accurate, have less inductance, low tempco, low DA, no microphony... as for distortion, good luck finding it (this guy measured it at -128dB on a 10nF)


So, C0G ceramics killed polystyrene, for good reasons. You can get a ceramic disc cap for through-hole, or just solder a SMD cap on the back of the board between the pads where the old cap used to be. As long as it's C0G/NP0 dielectric. Don't use the others like X7R, they are strictly for decoupling and will generate huge distortion if used in the signal path.

You can also use polypropylene (MKP) or polyphenylene sulphide (PPS).

No need to bother with mylar (MKT) caps, distortion/DA are much higher, and you're not out to save a few cents...