Q: my brake master cylinder leaks fluid but not all the time

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If I drive the car regularly the brake fluid doesn't leak. But if I park the car for a day or so, I lose brake fluid. It looks like it is coming out of the cap on the reservoir. I assume if there was a break in the reservoir it would leak all the time. Is the system pressurized and somehow forcing the fluid out? The fluid seems to only go down to a point where the brake light goes on in the dash. I'm stumped.and hope you can help. Thanks Doug...

My car has 46000 miles.
My car has a manual transmission.

Hi there. A crack in the master cylinder can cause the issue you’re experiencing. The system itself is not "pressurized" until the cap is closed and the pedal is pressed. When you’re driving, the fluid is continually in motion when the brake pedal is engaged; so it’s possible that the leak is worse when it sits. I would recommend having a professional mobile mechanic come to your location and complete a brake fluid leak inspection, so they can determine what’s causing the leak and recommend the right repairs.

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