Nissan Repair: 98 nissian, brake fluid and brake problem, vacuum booster, brake fluid

Question
The brake fluid tank or some part of the system is letting out the brake fluid, so I am constantly refilling the tank.  Today I started driving, braking maybe 2 times when I was backing out, and I noticed that the brake pedal was very soft.  So I turned off the car, and checked the brake fluid tank and sure enough it was almost empty, i guess it could have been empty.  I refilled it but the brake pedal is still very soft and doesn't work well.  I don't want to drive, because I feel like theres no control... what should I do?

Answer
Anastasiya,

If the brake fluid is not leaking onto the ground then it is coming out the back of the master cylinder and going into the vacuum booster.  Replace the master cylinder immediately.  Use Ford High Performance Brake Fluid since it has twice the boiling point of normal brake fluid.  It is DOT3 and you can get it from the Ford Dealer.  You have to ask for the High Performance Brake Fluid or they will sell you the regular stuff.  Buy three pints to do your car.