I had a similar problem. It's pretty easy to simply loosen the two nuts holding the master cylinder to the brake vacuum booster. Pull the M.C. out just far enough so you can stick a wire into the booster like a dip stick. If it comes up "wet' with brake fluid you'll know where the fluid went.

I ended up replacing the master cylinder (it was leaking into the booster). I used a bunch of rags to soak up the fluid in the booster and get it dry. The booster on my 107 has never been replaced and it's been 8 years since it got drenched with brake fluid. It still works fine.

Don't let the brake fluid get on any painted surface, it's like a paint stripper.

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1972 450SL
1982 300D Turbo