We’ve given you generic examples, and ways you can extend the life of the device.
There are no “exact” time frames, some manufacturer where better then others 20 years ago, thus we can not say: “Do X and Y and we guarantee 10 years”… I would bet, that some of your devices have capacitors that are already starting to prematurely fail. It would be best to carefully open up each device and actually inspect the capacitors for failure.
PS, One system that comes to mind, is the original XBox, if you have one, this device has an RTC circuit that uses a Capacitor, that is known to “fail” and actually take out the main board from the materials in the Capacitor:
In the end, we can only recommend procedures to protect your device, but unless you open it up and properly inspect them and personally maintain the PCB, it might not be for nothing…
Regards,