Yes, polystirene it was and loading it was. Some of well known factories used them, I believe it was Nac. I've been adviced to put them in my 965, but have been warned to solder quickly which I always is, no mather what I'm soldering. Nobody wants overheated pads and solder joints. Thats why good soldering equipment is worth money.actually, i've bought a few of those big 1uF WIMA but i still never tried them!
Regarding some good ones, don't know if as coupling caps (their capacitance values are way too low for that) but surely as loading caps (parallel between head's signal and ground) or into EQ networks, where you can be OK with capacitance values in the hundreds of pF or a few nF, a very very good choice would be the polystirene ones... but they need special attention while soldering them.
Anyone can comfirm thet polystirene makes a difference?