Well, I just went through my brakes due to this same issue. I've got all new fluid twice over, cleaned all pins and oem brake pads. I just ordered a new master cylinder but now I'm worried it isn't going to help.
Got my car in the shop after doing a simple brake job and they were concerned about the soft pedal.
Maybe you guys can help me figure out what I'm missing. The brake pedal has gradually gotten softer and softer as I've owned the car, but never has gotten to the point where I couldn't lock up the wheels.
Anyways I decided I wanted a firmed 'catchy' pedal again so I bled my brakes thinking there was air in the lines. That didn't do the trick so I replaced the master cylinder. After bleeding the brakes for 2 hours today the pedal feel is back to what is was before more or less.
Something that occurred to me a few minutes ago is that I could have a frozen caliper pin somewhere, I've heard of that causing soft pedal.
What is causing my soft pedal? It's driving me nuts!