Is there any test or way to tell if my master cylinder or brake booster is going bad in my 300e. I drove it to work yesterday and it was fine. When I go to lunch I noticed that it was real spongy. I checked the fluid and it was low. It wasn't empty but pretty low considering how I frequently check my fluids. Any suggestions?

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1972 220d gone lived a good life
1972 280se gone but not forgotten
1978 300D the best i ever had
1977 350se speed racer gone
1995 honda accord lx coupe victim of the growing family
1988 300e gone but not forgotten