Marlon

My brake pedal has always been soft, but brakes work even though pedal travel seems to go forever and it never really is firm at all. Also when releasing the pedal from a stop the rear brakes groan as if they are slow to release. I have bled the brakes twice with 22 psi pressure bleeder and the first time all 4 rear bleed taps spewed big bubbles, but no bubbles anywhere now. My 'guess' is that the master cylinder is at fault. Master cylinders are 'cheap' relatively speaking - any thoughts on replacing the MC or anything else to look at before jumping into it - or simply having it done??? No codes nor CELS - although occassionally I bairly catch a 'brake fluid' light even though the brake reservoir is very full.