I think either the coil (which is oil-filled and sealed for life) is leaking, in which case you should replace it immediately as it will either stop working or possibly catch fire soon, or the brake master cylinder is leaking, probably where it joins the booster. The booster is the giant donut thing and the master cylinder sits on the front of it, and the brake fluid reservoir sits on top of the master cylinder.
If it turns out to be brake fluid, make sure you thoroughly clean it off everything as it is corrosive and will eat the paint and then start rusting the metal.
