Reviews of OEM Volkswagen brake cylinder

Brake master cylinder was absolutely shot and was not doing its best with the new GLI brake setup, so I managed to swap in a GLI 10.1" rotor type setup and it worked out very nicely.

Next job to tackle is the weak brakes. Going to start with a brake master cylinder replacement because when I'm sitting at a red light, the pedal goes from hard for about 20-30 seconds to softening up and going to the floor with no clamp force anymore until I pump the pedal again.

I removed the brake master cylinder and wanted to inspect the internal seals... A faulty master cylinder would be spongy and soft to push its piston all the way in. A good master cylinder would be only soft when the lines are open, and would be hard, or require more force if the holes were plugged/sealed/closed. I used rubber stopper to plug the holes and performed the test: As you can see in the picture: in both tests it took almost same amount of force to push the piston. That indicated an internal leak, and a faulty master cylinder.