life span/failure rate of filter capacitors?

Each 10degC temp increase shortens capacitor life by 2.  It is simply drying out of electrolyte.  Drier capacitors have higher ESR.  At certain point current thru capacitors causes internal temperature increase.  Temperature increases ESR and higher ESR increases power dissipated inside increasing temperature further.  It is Avalanche effect that can cause explosion.  To prevent serious damage all electrolytic caps have some form of pressure relief - either rubber plug or cross cut that weakens one side.  Hot capacitors should be replaced as soon as possible.

@audioman58   IMO capacitor dry out powered or not.  Unpowered capacitors are likely at lower temperature drying slower.   Electrolyte tends to eat out dielectric (aluminum oxide) reducing breakdown voltage, while presence of the voltage rebuilds this layer.  Gear (or caps in storage) unpowered for many years (likely >5), should be powered at lower voltage (like half) increasing it slowly (Variac) over at least a day.  Unfortunately SMPS often don't work at all below certain voltage and output capacitors cannot be fixed that way.