RCA 6K Puzzle

Greetings to all! I'm writing to ask for help with my RCA 6K. I restored this radios several years ago and use it in my workshop as my daily driver. It's got great sound and terrific bass. Anyway, about a year ago, while listening, the volume would suddenly get REALLY loud, the volume control still worked to raise and lower the volume, but even with the volume all the way down, it was still fairly loud. Turning the radios off and on again would return it to normal. It may happen in an hour, a day, a week or more, but always happens. I removed the chassis, checked all the connections by tapping and prying with t plastic tool and could not get it do it. I cleaned all the tube pins and sockets and put it back together. It seemed fine for a few weeks, then the same problem. A few weeks ago, I took the chassis out, replaced the volume control and changed-out all the tubes. I ran it for two weeks out of the cabinet and it seemed fine. I put it back together and used for a little over a week and then, tonight same problem. It's definitely not a bad connection as I re-soldered almost every joint and banged the chassis and every connection. It's not a tube or the volume control.
When the volume rises, it goes quite high with no static or rumble whatsoever, it's as if someone threw a switch. Turning the radios off and on again always returns it to normal. Does anyone have a clue what else may cause this problem? I've done and checked everything I could think of. I even hit all the connections and parts with -50 spray.

If your light dims Then this may be of interest.
This is from CASE HISTORIES in Radio Troubleshooters Handbook.
"RCA 6K-2, 6G-10
Intermittent____1) small rivet in center of band pilot light cutting off of signal and dial light "SHORTING TO GROUND""
And my own opinion (LOL) a resistor or CAP value may be changing due to heat, since it seems to work out of the cabinet.