1989 Honda Prelude CLUTCH MASTER CYLINDER OR SLAVE CYLINDER

I PUSH THE CLUTCH PEDAL IN AND IT STAYED ON THE FLOOR CHECKED THE FLUID LEVEL (LOW). THERE IS NO APPARENT SIGN OF A FLUID LEAK ( NOT AT MASTER CYLINDER OR THE SLAVE ) HOW DO I TELL WHICH ONE IS FAILING ? THIS CONDITION HAPEND TWICE IN A FEW DAYS. I ADDED FLUID AND BLED THE SYSTEM IN BETWEEN FAILINGS AND BROUGHT THE SYSTEM BACK.