Hello: Seems some confusion of self healing caps vs RIFA failure issues. My understanding: .....
1/ "self healing" applies to certain metalized film caps: where failed dielectric spot burns away and leave a void inside the wrap. That leaves a small hole, thus clearing the short. Both dielectric and foil must be very thin and designed for that. Normally the self healing occurs in current limited circuits.
2 Certain RIFA and similar 1970s..1980sVDE X and Y caps plastic encapsulating material looses the plasticizer over decades of time and heat from a PSU. These have a rectangular shape and yellow translucent molded plastic encapsulation.
3/ The result is cracks and crazes in the encapsulation.
4/ The cracks allow ingress of humidity. Ultimately this leads to failure under mains voltage, especially in 204 V mains locations, less so in 120V (USA CA) or 100V (Japan) zones.
5/ No "self healing" can occur in those failed caps, The EMI filter use of X and Y caps means that the mains is directly applied with little or no current limit. The plastic and dielectric are flammable thus cap has a catastrophic failure, possibly explosively or fire.
6/ In 120V zone, I have not experienced any RIFA failures in many decades of TEK and HP instrument use. I have no equipment in Paris at 240V that has such caps.
7/ Many Schaffner and other IEC line receptacles /EMI filters and some EMI filter modules have such caps inside thus their failures.
I view the materials problem as an unexpected consequence of the particular plastic composition, aging after decades. I doubt the manufacturers or plastics suppliers ever had envisioned this deterioration 30..60 years after manufacture.
The perils of using vintage test equipment!
Bon Chance,
Jon
Jean-Paul