Wheel cylinders go bad they leak. Fluid gets past the cups and...at least that is not the issue. MC goes bad and fluid leaks past the cups and no pressure to move the wheel cylinders. I would pull the MC and take a good look at the inside. You might save it with a hone and some new parts. Cheap. You can bench test it with out too much hassle and save the cost of a new one. If it needs to be sleeved or replaced you are half way there. Do the bleeding first to make sure there are no air bubbles. But if the MC is bad you won't make much pressure and it will be frustrating to get all the air out of the system. Take your time and see what you have. Your life and some others may depend on your work. Take your time.
