Could be carbon wipers on the volume pot or balance as Phil(Picard) has mentioned. Problem is spraying electrical cleaner down the spindle often doesn't reach the wipers. If you're handy with a screwdriver you can lift the lid and take the pot out, prise the back off them and clean the wipers directly.
It would easier to find the problem if you dismantled the unit, waited for the channels to fail and poked around with a multimeter to see where they go dead. Don't do that unless you have a clue about the potential dangers lurking inside.
Should have read your post properly, intermittent static would be difficult to diagnose with a multimeter.
I'm happy to get stuck in as I'm essentially going to try and fix this for fun/as a project.
I'm not going to do anything when the unit is left on though as I have no idea what I'm poking.
Could be carbon wipers on the volume pot or balance as Phil(Picard) has mentioned. Problem is spraying electrical cleaner down the spindle often doesn't reach the wipers. If you're handy with a screwdriver you can lift the lid and take the pot out, prise the back off them and clean the wipers directly.
It would easier to find the problem if you dismantled the unit, waited for the channels to fail and poked around with a multimeter to see where they go dead. Don't do that unless you have a clue about the potential dangers lurking inside.
Should have read your post properly, intermittent static would be difficult to diagnose with a multimeter.