In article ,
says...
I tend to define “breathing” as a uniform, repetitional slow time
constant of change, while what you describe is random in its
occurrences.

Had to choose one word for short title description, and hopefully
described it better in the body. Could have said "jitter", but not
sure if that fits either.

Well with the SS we know it’s a sheltered model and with the 27 it has
a 27 inch pic tube, and with a 12 suffix its at the very bottom of the
design/features line or a table model.

Actually, it's a rather nice floor model with stereo I/O and glass
doors and shelves in the bottom for VCR or component audio. I thought
the "service number" SS2712VK9 would be sufficient, but if it helps
serial number is 091-25500260, manufactured December 1990, "module
replacement number" 9-896. Is the module replacement number what
passes for a chassis number in Zenith circles?

But anyhow, going on in the blind. Have you observed a still/stable/
fixated enough pattern to ascertain if that hoz compression is squeezing
in equally from both sides. Or is there is a coke bottle type of side
compression, with the most compression being in the center and bowing
in less at top and bottom.

It is changing about the same on both sides, and the amount of pin
correction does not appear to be changing. As near as I can tell
without a schematic, it appears to use the single big diode modulator
pincushion setup. But it also has a big NP elctrolytic that most
makers do not use. Maybe I start there since I can read the value
and happen to have one handy. Some of the other parts like the big
safety cap, for example, just have house numbers so I am not totally
sure what to use for sub. I hate when they do that.

I suspicion that you are starting to experience an intermittency of
connection in a solder joint on a hoz or pin ckt component that
inherently runs quite warm or carries a high pulsed current level thru
its path, or is in the close proximity of another warm running
component. What I might suggest is getting an ~ ¼-3/8 in dia solid
plastic rod that is ~ 1 ft long

Horizontal drive looks plenty big and doesn't seem to change when it
is acting up, and the HOT doesn't get excessively warm, so I think it
is being switched hard enough and the problem is somewhere downstream.

I have a small paint brush with plastic handle that I use for both
cleaning and tapping, and nothing seems sensitive. I've inspected
the soldering pretty close and sucked off and resoldered anything that
looked questionable plus a few that didn't. Replaced on principle a
cap that had leaked a bit even though it checked good. So far nothing
has affected the problem.

The chassis/module with the most troublesome pin circuitry is to the
right front corner where there is a troublesome pair, of a hot running
pincushion diode and a vertically mounted pincushion coil.

Roger the big diode and coil. I'll give them the third degree...

And about the big safety cap that only has a Zenith number on it -
I'm reading about 4700 pF and ESR looks reasonable. I'm guessing it
might be a 1600V polypropylene if I have to make a stab at a real
world part. Does that sound right?

Lastly, and you do know *not* to French Kiss the very well insulated
red high voltage wire going up to the picture tubes top insulated ultor
connection from the high voltage transformer don’t you

The big red wire has mostly not been a problem for me, but I am good
at finding pinholes in the smaller white focus wire (bszzzht!) ;-)

Thanks.