Help

What's this thing with the yellow knob? The writing's in German & it's leaking on my friend's car. I told him it's the bumper fluid, but he thinks it's blinker fluid.

Is it ok to drive?

http://zip.4chan.org/o/src/1234662856247.jpg

What's this thing with the yellow knob? The writing's in German & it's leaking on my friend's car. I told him it's the bumper fluid, but he thinks it's blinker fluid.

Is it ok to drive?

http://zip.4chan.org/o/src/1234662856247.jpg
That is the Brake Fluid Reservoir - DOT 4 Fluid