So this is my current thinking about this problem:
1. I think that the issue has been pretty well isolated to the HV transformer, HV multiplier, and regulator circuit.
2. It sounds like the regulator is trying to do its job, which means that most of the components are good.
3. It also sounds like the regulator is not working especially hard, which suggests that the HV transformer is probably okay.
4. That leaves a couple of HV parts, and the transistor that drives the primary winding (Q1318) as suspects.
5. All the remaining suspects are inaccessible without removing the main interface board.
I would be overjoyed to be proven wrong on that last statement, but I'm perfectly willing to undertake the task of disassembly. This was meant to be a parts scope from the get-go, and everything I'm doing on it is in the interest of learning and practice.
-- Jeff Dutky