Thanks, Tom -
I read the thread that you referenced, and borrowed a high voltage meter . I'm seeing approximately +2700 volts on the cathode of the CRT, and the meter moves a very slight amount higher when measuring the grid. The intensity control has absolutely no effect on the grid voltage.
I see in your tests that the grid was driven -50V wrt the cathode, which pointed towards the bad CRT. My results seem to lead me back to the DC Restorer circuit.
I'll see if I can find replacement diodes and caps, and see if that resolves the issue.
Thanks again for your help!