The front master cylinder on my brand new 300 is slowly sweating brake fluid through the membrane vent hole. Is this normal (e.g. happening because it was overfilled or something), or do I need to insist on warranty service? I complained about this at the first service but the shop chalked it off as condensation from the top of the membrane. It happened again after being parked for a couple of weeks, and it's definitely brake fluid. Thoughts?