I was thinking corrosion, rust, ???

Rust is iron oxide and will only form on iron or steel. Corrosion is a
different matter, but you can rub or spray corrosion off. The only way coax
deteriorates is in sunlight or with water inside the shield. Age is a
second order factor.




on a coax connector, or
connector anywhere (especially connector tray - radio), for that
matter. Even you agreed that replacing the coax "may work" and that I
would only be out a couple of bucks, worst case.

Yeah, as well as throwing salt over my left shoulder has kept me from being
trampled by hippopotami all my life, but I don't think replacing the salt
shaker is going to have any effect.



Your description of
cutting the coax at a 45 degree angle led me to think that you might be
questioning the coax "connector" to radio or antenna or at least be
keeping it on a list of suspects.

No, I was telling you to do that so the square-cut coax wouldn't hang up on
the grommets as you pulled it.





My advice is to tune in a constant signal ... like an atis or awos and
start
moving things around briskly. When the signal fails or comes back after
failure repeat the jiggle. Narrow down the jiggle area.

I've been using the ATIS at SAC as my constant signal, and have been
forcefully pressing the radio in and shaking it from side to side to
see if I can get it to come in, so much so that the LED's dim on the
radio as I'm pushing it in.

Do you intend to destroy your radio in the fixit process?



That's never got reception to come back.
As far as other things, which I assume you are talking about wires
behind the panel, I can certainly give that a try, once I can figure
out how to do that without putting my self into an unintentional
unusual attitude. I'm 6'2" and about 2 bucks, so I can barely get
behind the panel when the plane is parked safely on the ground, let
alone 5000 feet and 100 kts.

You CANNOT do troubleshooting at 5K and speed. You HAVE to do it on the
ground. THe easy way is to pull the front seats out and lay on the floor.
I'm 6-3 and two and a quarter, and this is the only way I can troubleshoot
any airplane except a heavy with a radio rack in the belly.




I REALLY do appreciate all of the input, and am not TRYING to be a
knuckle-head about all of this! I'm just trying to interplote the
input I am receiving and do things that are within my capabilities.
And in this case, my capabilities don't seem to cover a very broad
spectrum!

You need to get the airplane to a place where you can get at the radio with
a constant signal. You also need access to tools and such when you DO find
the problem. I think I've got an old com test set around here somewhere
that radiates a constant low level signal on 122.8, powered by a 9 volt
battery. If you'd like to come up to Grass Valley and borrow it, I'd be
glad to loan it to you ... if I can find it.

Jim