4 or 5 years is no problem. 8 or 9 of zero use is starting to get to where you should worry a little. Over 20 you need to consider replacement. This is my experience as an EE.
There are thousands of capacitors for sale at Newark and Digikey that have been on the shelf for years, waiting to be sold and no one uses a variac when they power them up for the first time. I have powered up MANY converters and power supplies in my lab that sat for at least a decade and there was never any issue. You are worrying way too much about this. Just enjoy the music.
Arthur
There are thousands of capacitors for sale at Newark and Digikey that have been on the shelf for years, waiting to be sold and no one uses a variac when they power them up for the first time. I have powered up MANY converters and power supplies in my lab that sat for at least a decade and there was never any issue. You are worrying way too much about this. Just enjoy the music.
Arthur