Well, Im glad you found a fix, IMHO it would have been a shame to put a SS module in this iconic set. To me, the symptoms you describe had the earmarks of capacitor failure, not inductor. Im sure you have checked these but IMO might be worth checking again. One possible culprit might be C71, the 4.7pf between plate and grid of the oscillator. This cap will heat up on its own due to the combination of high frequency and high voltage, and could start leaking if not fresh and rated at least 1kV. A leak here would bring down the HV in short order.
Finally, I once built a 500kV Tesla coil, so I know about this stuff..
