Help Brake master cylinder

[Vanbursta]

Quick test.

If the fluid level is not dropping:-

Sit in the car and stomp on the pedal quickly, if it goes hard then travels slowly to the floor it will be most likely be Master Cylinder. If you push it gently and it travels to the floor immediately, could be a seal leaking somewhere. Or a flexible pipe ballooning.

If the fluid level is dropping:-

There is a leak somewhere, you need to find it. Sometimes the fluid can leak past the master cylinder seals into the servo, in which case the car will have blue smoke out of the exhaust (the brake fluid gets sucked into the inlet manifold and burns off). Could be leaking at any (or all) of the following

Flexible pipes / connectors
Caliper / pipe to caliper connection
Perforated brake pipe

Wherever it's going it will be immediately obvious when you find it.

I wouldn't drive the car until you've fixed it, if you have an accident knowing the brakes to be faulty, it could be very bad.