2012 XC90 3.2 AWD
Miles 132000

Issue:
Soft / Spongy pedal. You can work the pedal to the floor over a 2-3 minute period. The brakes do work, the car stops. But the pedal moves too much before the brakes grab in a solid way.

Notes:
No lights or codes.
Brake pads and rotors are in good condition, about 50% through their lifespan.

What I have done so far:
Blocked off the master cylinder lines with brass plugs. While blocked the pedal is a rock, the rock of gibraltar! I am assuming (I know) that means the master cylinder is not leaking internally / bypassing.
All new rubber brakes lines (Genuine). They were original, so I was happy to replace all of them. No difference in the spongy pedal.
Pressure bleed system from master reservoir. Pushed about 2 quarts of new fluid through this beast.
Visually inspected the entire system for leaks, under dash, all line connections, calipers, bleeders, etc. No leaks, and no loss of fluids while driving the car for a few hundred miles. The brakes do work predictably.
Inspected caliper mounts for cracks or other rigidity issues. Nothing observed.

I am thinking the leak down is in the hydraulic portion of the ABS Module. Perhaps returning the fluid to the master? I don't know the architecture of the hydraulic system within the 12 valve hydraulic block on the ABS Module.

I have seen one Youtuber that resolved a spongy pedal in a V70 by replacing the 12 Valve Hydraulic unit with a used one.

Questions:
Anyone have a Volvo procedure testing the hydraulic integrity of the ABS 12 Value Unit?
It seems nobody Hydraulically rebuilds these units? Plenty of people are reprogramming.
Seems Volvo never sold the hydraulic unit separate from the actual electrical module? Agree?
Any recommendations?

Of course I'd rather not spend $1800 on a new unit from Volvo, but I would not mind too much as long as my diagnosis was correct. The car is really clean and I have owned it and taken care of it for the last 50K.

Your input is appreciated.

Thanks - The Machinist