I meant that the tone, balance etc. circuits, where the original caps are left, are no longer active. New wiring has been run to make the amp a simple power, volume & source affair, it's just that the wire, resistors and caps are physically still in place.
I had a power tube go red several years ago (replaced the pair) with no other issues 'till now. I don't have access to a tube tester, but a new quad of el84s would be cheaper in the long run than a repeat of this.
It was nice of you to be a good fan and let him continue on incognito.