I have replaced master cylinder and front grommet on bottom of reservoir shows leaking brake fluid like the one i replaced. Bled all wheels numerous times. Gravity bled as well. Booster is fine. Still have soft pedal. Brakes work fine. But pedal is still soft. I even bled abs module manually.

 

Most newer scan tools ex( snap on, gm tech) and some higher end scanners have an automated bleed programed into it, some combination valves have to be bled if you have that kind of system. Sometimes you can find your system information on alldata or maybe even a youtube video!