Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Hello, if you don't see any external leaks it is most likely leaking at the rear seal of the master cylinder and going into the brake booster.
To check this you can unbolt the master cylinder from the booster and check the rear of the cylinder.
Be advised if that is where it's leaking, the brake fluid will damage the rubber diaphragm in the booster causing it to eventually fail.
You're welcome, let me know if that's not it and we can work further if needed.