Leaking brake fluid.
If your brake fluid is consistently going low then there is a leak. If it goes low to a point and stay there then it may be typical of a disc brake system. As disc brakes wear out the fluid stays in the caliper causing the fluid to appear low. Once the brakes are repaired the fluid returns to the correct level. If the fluid is going down quickly then all of the wheels need to be removed to find the leaking parts. Most of the time the leak is in the rear brake wheel cylinders. These commonly fail and become the main point of fluid leakage. They would then need to be replaced. If you plan on having this repaired, consider YourMechanic, as a certified mechanic can come to your office to find the leak and repair the vehicle.
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