92 Civic LX with 241,000 miles, all stock.

I been having an issue with my front brakes. When I apply the brakes ALL THE WAY to the floor my car won't stop...it'll slow down a tiny bit...but never stop.
When this happened I was going about 40 MPH, and had to press the brake pedal MULTIPLE TIMES to get the feel of the brakes back(pressure to the brakes) to slow the car down, and use my emergency brake to stop.

So tonight I did some tests:

- With the car off, I pressed the brake pedal several times(all the way to the floor), and felt pressure in the pedal building as I was pressing it (No Stiffness in the pedal), then pressed and kept the pedal down and turned the car(engine) on. The pedal went down slightly, when I let go of the pedal it returned to it's normal position(high position....not to the floor).

- Afterward, I opened the hood and with the engine on, disconnected the vacuum line to the brake booster, and the engine started running a bit rough. I put my finger over the vacuum line and the idle returned to normal.

- Checked my Brake fluid level, it's full and same level it's been for months. Its kinda dirty...but full!

- Checked for leaks on Brake Booster and Master Cylinder visually and with my finger(wiping with finger)...No leaks/ No wetness.

- Checked inside of wheels for any brake fluid leaks visually....no leaks/no wetness. Checked brake lines as well....No leaks.

My brakes are not really spongey...it just seems like I need to keep pressing my brake pedal(while driving today..and only today) to get enough brake power to at least slow down.

I'm not really a professional when it comes to the braking system. I just know how to change the brakes, rotors and flush the brake lines. And I did those tests above because it's what I found online, but don't really know what it all means after I did all that.
So can someone help me out to find out what it could be...or what it couldn't be?
I would really appreciate it!

 

There could be air in the system, but more likely the master cylinder is toast and needs to be replaced.

 

Hmm....Would the Brake Booster cause this as well and should I replace it along with the master cylinder?
I remember replacing the master cylinder twice over the last 5 years(due to external leak), but it looks fine now(externally).

 

Absolutely not.

It can also leak internally, which is almost surely the current problem.

 

Ditto the above^^^ blown seal in MBC, you may see indications of this on the inside of the car, at back of MBC where rod goes into brake cylinder, leaking at that point indicates a blown seal. may be just a small leak. 94

 

Thanks guys! Already ordered on Amazon...will install during the weekend.
Appreciate your help!