1991 Mazda B2200 brake pedal goes to the floor before brakes engage

1991 Mazda B2200 2.2L mileage: 180,000. When I apply the brakes the pedal goes almost to the floor before the brakes engage, (when this fist started if I pumped the brakes it helped but that doesn’t work as well anymore), and they seem softer when they engage. If I push harder with my foot it gets a little better, but not as good as normal. I checked the fluid and it is fine. My friend suggested the master cylinder, what do you think? Great site by the way!