So I went on starting diagnosing the syncro's oil pressure light/buzzer
issue.

The control for the Dynamic Oil Pressure Warning System needs to see two
things: the .3 bar sensor open (no ground) under 2000 rpm and the .9 bar
sensor closed (grounded) over 2000 rpm.

I figured the best place to start was looking at the ground connections on
the driver's side of the engine bay. Sure enough, the braided ground strap
was corroded and broken where it bolts to the body. Also, the handful of
other grounds there and bolted to the body near by were also severely
corroded. I took them all off, put on new terminals, and cleaned up the body
where they connect. Then I cleaned up the braided ground strap and crimped
on a new terminal.. I hooked everything back up and then coated them with
dielectric grease. For shits and giggles I cleaned up the o2 sensor
connection, it had some corrosion as well, and hooked it back up.
Disconnecting it had cured the poor running problem and let me drive it
home, but I thought I'd see if cleaning the connection might fix it.

I hooked the battery up, turned the key and it started right up. I let it
warm a bit then revved it to about 2500-3000 rpm. Guess what. NO OP LIGHT
FLASHING AND NO BUZZER! It was a ground problem all along. And to add to
that, it ran great after it was warm, so the o2 sensor wasn't the problem,
the connection was! Woot woot! I drove it around and it drives great, there
is a slight vibration around 45-50mph (thanks Scott, you were right) which I
think might be worn u-joints causing the driveshaft to be off balance, but
nothing too severe.

Now I just need to finish detailing the inside and troubleshoot the no turn
signal issue and the tail light/reverse light problem. Could be bulbs, I
haven't looked yet.

Woo hoo, $500 Syncro continues to be the deal of the century.  :)

Brendan