I firstly assume the cap is an electrolytic.
If it's a signal/ decoupling cap, then it will most likely expire due to over voltage, although it can also expire if it is near a source of heat.
It is a filter cap it could also expire due to poor ripple current rating, which causes self heating.
I've seen quite a few piece of equipment where the voltage compliance of the caps is exceeded in normal use.
When you replace the cap I would go for 105degC cap (regular caps are rated at 85degC; all things being equal the 105degC cap will last 4 times as long as the 85degC cap) rated at a higher voltage.
Of course there could be another problem with the unit which is causing the cap to expire, but I would go down the uprating route first.
