I appreciate your concern with respect to the danger, I used to work on large CRT displays, they too had large voltages. I have tried discharging the Hi-Voltage cap before, it doesn't seem to retain a charge. Someone else commented that it might have a bleeder resistor.
Just a quick review: The unit heats everything well, with the magnetron disconnected there is no buzzing. If the HV Diode was shorted would the buzzing continue with the magnetron disconnected?
I do not have any service literature, can you help me identify the HV Rectifier? I presume it is connected to one of the leads from the HV Xfmr and one of the HV Cap leads. Am I correct?
Thanks in advance