3 months later, I have resolved the TFV12 leak issue I've been having. I replaced and double checked every O ring in the atty, and just when all seemed good, blorp. Entire tank running down my mod/in my pocket.
Infuriating. it made no difference what coil was in the atty, factory/dual/triple RBAs, same thing always randomly eventually happened.
The culprit? The O ring that you cannot see. The 12 uses the same base design as the 8. On either of those attys, turn the airflow ring in the base. Notice anything? The airflow ring has a slight, even resistance as you turn it, because there is a seal inside the base, That is what causes the friction you feel.
That seal, is not accessible, as the base is pressed together from 4 parts. (bottom, top, airflow ring, and the seal) Not accessible that is without destroying the base. During the pressing operation, you can easily imagine what happens to that O ring, if it is slightly misaligned. it gets cookie-cuttered. It will partially seal, for a while, until the tank pressure, or vacuum forces the juice past, then gravity does the rest.
I obtained a different base, and not a single leak. I even switched all the parts including the center pin, Not even a hint of a leak. Yet.
Eventually the hidden O ring will degrade, or wear enough that they all will begin to dump. The TFV8s as well. And no way to repair them. Bastards. This TFV12 is likely my last Smok atty.
So, if like me you have been tormented by this tank, and its tendency to leak like the Titanic, although in a purely random manner, know that its not you, its Smok. And if even one person suggests that it HAS to be your wicking, just smile, and ask if they will trade their base for yours...