Last night I was able to find the washer is SL6-D which I believe has been
causing the problems (first, the threshold short from earlier running, and
later TREF problems).  I was able to spot its reflection against the
kapton tape of the ID extrusion, under the CV board hanging near the
SL6-370 red connector pins.  I found it on the first faraday cage I removed,
and have thus used up all my good karma for the next few years.  Tomorrow
I may stay in bed with the shades closed.

I reconnected all u-coax, but have not successfully checked it with
COTASDQ calibrations...I'll try again in the morning.