I just got my first bike, a 1983 Kawasaki KZ 750, so I don't know much about them yet. But I was examining it trying to learn what I could about it. I noticed a box on the handlebars, attached to the front brake lever. On the front of the box was a little circle that looked like a button. Like an idiot, I pressed on the circle and it broke and pushed in. A dark fluid came spilling out. I assume it is brake fluid, does anyone know for sure? Also, how important is it that I replace this? I mean can I ride safely with it like this or is it critical? By the way, the brake still works just fine, I don't notice anything unusual about how it performs. It did lose quite a lot of the fluid though.