Can a brake master cylinder leak internally?

Yes, a brake master cylinder can leak internally. This occurs when the seals inside the master cylinder wear out or become damaged, allowing brake fluid to bypass the seals instead of moving the fluid through the brake lines. Symptoms of internal leakage may include a spongy brake pedal or a gradual loss of brake fluid without visible external leaks. In such cases, the master cylinder typically needs to be repaired or replaced.