[MrMCar]

In a nutshell, your car has 4 wheel ABS/DSC. should the left rear start to encounter ice on braking, the DSC module will release the pressure for the left rear brake caliper. Currently it sees a connection issue with the electric solenoid of the left rear inside the DSC unit.

Could be the module itself? (Most likely) or the valve inside the metal housing is bad? (Less likely.)

You can go to a junkyard, find the same module used and screw it on. Chances are it might have another fault, but not likely to have the SAME fault.
If the fault is different, you need a rebuilt module. That's the black electrical part that screws onto the front of the DSC module.

 

[MrMCar]

My reasoning for trying a used module was to see if the fault is with the electric part, or inside the hydraulic part.
We have many used (bad) DSC modules here at the shop. We have them on the shelf with the faults listed on them.

If your car was in my shop (Fault 2F) I would grab another module with a DIFFERENT fault. Cycle the key and if the same #2F fault returned I now know the issue is likely inside the hydraulic unit. If the fault changed to the one listed on the outside of the bad module, I now know that the module on your car is bad.

Given the amount of goo you have inside the bottom of the master cylinder reservoir, I would be doing two brake flushes with a fast drive on a open dirt road with a lot of heavy brake applications to flush out the goo from the DSC hydraulic unit. It will eventually all come out, but may take several brake flushes.