After week two, it was decided that the most effective way of fixing the PET is probably to replace the caps, on the assumption that at least one of them is bad -- it's the most likely failure mode when a bit of poking doesn't show anything obvious.
[original factory documentation] (et seq) lists the following caps:
|count||item number||ref des||original note||voltage||capatice||type|
|5||40||C1,16,17,23,24||13||25V||10uF||low leak elect.|
|4||41||C6,8,10,51||13||50V||1uF||low leak elect.|
Note 13: "For substitute part, see part substitution index, part number 321233."