Sudden Soft pedal AND
no external leak = MC is bad or maybe you've boil the fluid.
MC then replace MC
If you Boiled fluid in street cars then fix what caliper is dragging and flush old fluid.
Get a cheap IR meter to quickly find a dragging caliper.
See my Cave, IR thermometer
and Brake Fluid
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)