Should capacitors on old ECM be replaced?

[Dave9]

if equipment containing electrolytic capacitors, typically found in its power supply, is used often the capacitors will not dry out and fail. If they do go dry, they can be "reformed" using a Variac.

You are confusing two different failure modes. Electrolytic capacitors can dry out over time and fail, but this does not happen from lack of use, happens either way, somewhat faster if it sees a lot of thermal cycles or perpetual high heat.

Instead, lack of use for long periods (years at a time) with aluminum electrolytic caps causes a breakdown of the oxide layer on the aluminum foil and they become electrically leaky. This can cause rapid overheating and failure, and a lesser temporary concern is a capacitance drop.

It is this oxide layer that you'd restore by applying a low voltage over time with a variac lower voltage supply, but that will not recover a capacitor that is too dried out.