First let me start by thanking this great forum for teaching me so much about my car. This truly is a great site.

Now on to my question. I've searched high and low and have come to a few theories, but have come to no conclusions yet.

Problem
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First off the Brake failure light is on. Under normal driving conditions with an average amount of braking there appears to be no problem. The brakes are firm and sturdy. But the problem appears when you are in stop and go traffic. When the brakes are pressed often and repeatedly, the pedal becomes very hard and stiff making each successive press of the pedal a harder effort to make the car stop. I've read that if the pedal goes soft it's the MC. So I'm guessing it's the booster.

How could I test at home all these components, Distribution block, MC, booster, sensor? In regards to the MC I saw a few posts that talk about the braking and reving test. I haven't tried that yet, but I will tonight. For the booster I read to perform the Bentley Manual Booster test, but I can't find the steps anywhere. I only own the Haynes book. Now the other three I have no idea how to test.

Are there any other parts that could be bad? The fluid level hasn't moved in years, so I doubt there is a leak. I also haven't bled the system in about 4 years, which I'll do as soon as I can diagnose this problem. Also, another fact is that the Brake Failure light came on right when I changed the battery on the car. I've tried disconnecting the negative battery line for a few minutes to reset the light but it stays on. I'm not sure if this has anything to do with it.

Thank you in advance for your help. Sorry for making the post so long, but I wanted to present my case well.