Just an update...
So having the TCU open I checked the continuity of each of the pins and various places on the board.
I wasn't able to find any clues while wiggling or squeezing the connector or pins, unfortunately.
after a quick "spray and pray" with the contact cleaner, I plugged it back into the car turned the key to the on position (engine off) to check the bulbs on the cluster, and sure enough there was no AT light appearing at all.
Got down under the steering column and moved the wires around, etc. and like before I was able to make the AT light flicker as I moved the wires in certain positions.
Narrowing down the most sensitive area I was again confident that it was the TCU side connector, not the wire..
So, I figured "bugger it" and fired up the soldering iron. With a tiny bit of solder I heated up each connector pin on the PCB quickly but just enough to see the solder turn to liquid and hot enough to stick to the pin, and then remove heat and onto the next. I could only do this on the underside, as the top side had far too many components in the way and even with a narrow solder iron I was still unable to reach the points.
After a quick spray with contact cleaner to remove any flux residue, I took it back to the car, plugged it in and switched the car on (engine off).
The AT light came on instantly and stayed on. Moving the cables around the light remained on.. however there was a certain point where the light would still flicker, but this was very minimal. It was a huge improvement.
Started the engine and the AT light does its usual on for 1 second and then turned off.. and remained off for the 30km drive into town and back with a few starts and stops. This is the standard behavior of the light, for those not familiar with phase 1 4eat.
No CEL, no flashing AT Light codes.. no random on and off while driving.
So I'll take this as a win for now.. Though this isn't the first time this car has had me feel like I cracked the issue only to start again the next day, so I think I'll wait a few more days before I celebrate.
Hope my dilemma can help anyone else that may have a similar issue.