...I swear at least once while wiggling the front panel back and forth the grid circuit meter worked correctly. Is it possible... there's a short internal to the grid current meter, maybe to the lamp circuit? May have to tear it apart.
That is part and parcel of troubleshooting.
Never overlook something like that, for in effect, it means that you have pinpointed the area of the problem.
Good on ya for going in there and investigating the clue.
Or, as I like to say on the test bench, "She's talkin' to me..."
Then all I need do is figure out what it is she's tryin' to SAY.
All these decades of repair, I've learned that it is great to have lots of neat test equipment, schematics and service manuals plus the experience and knowledge to use them well, but if
asked to think about it, I'd say a goodly number of successful troubleshooting and repair came
down to using the human senses, mechanical intrusions to see what happens when you flex, poke or even lightly drop it back onto the bench from an inch or two, just this sort of thing as found here. Eyesight, sense of smell, ability to sense excess heat without actually touching parts that may have high voltages riding on them. Plus the reasoning of just plain common sense. You did well.
I love it when the plan comes together.