There are two sets of internal seals and a rear seal.
The internal seals can fail and the cylinder will retain the Brake fluid, it just wont work correctly.
Look for leaking fluid at the slave or master cylinder.
Is a bad thing and requires IMMEDIATE REPLACEMENT OR REBUILDING OF THE MASTER CYLINDER TO PREVENT SERIOUS INJURY AND OR DEATH
Master cylinder is bad and appears to be coming from the booster.
A symptom you almost always feel is a brake pedal that will not hold. You stop, hold the brake, and the pedal will slowly move toward the floor. This is a sure sign the master cylinder is bad. A leaking master cylinder or one that sticks, is also a sign is is defective. When you replace the master cylinder replace all the brake fluid in the brake system and bleed the brakes. Moisture in the brake fluid will destroy a master cylinder and this may be why it failed.Brake fluid leaking from the master cylinder. When you stop and hold your foot on the break the brake pedal will slowly go to the floor. Either of these symptoms means your master cylinder must be replaced.
That depends on where it's leaking out; if it's at the master cylinder, you have a bad master cylinder, if it's at the wheel cylinder you have a bad wheel cylinder if it's at a caliper... well, you get the idea. If you know how to repair a master cylinder, wheel cylinder or caliper, you can often get by with a little savings but it's usually best to just trot down to your local auto parts retailer and get a new or rebuilt one.
Normally you will see moisture, or fluid leaking from the master. Need more help contact me through my board and I will try to help.
The gasket to your clutch master cylinder is probably broken or cracked. or your master cylinder is bad.
the leak between master cylinder and booster is where difference type of gasket is worn out depended on the type of your vehicle...older vehicle usually have flat gasket but mostly have O-ring Gasket the need to be replace. you have a bad master cylinder its leaking fluid into your booster the seal or oring is just to prevent vacuum leak change master cyl before the fluid attacks the booster and you spend another 170.00
After you have located the clutch slave cylinder, have someone depress the clutch pedal. You should see the piston of the slave cylinder extend somewhat. If it does not, either the slave cylinder is bad, or the master cylinder, or, there is not enough brake fluid in the system for it to operate properly. Check the level in the master cylinder. If the slave cylinder is leaking profusely, it is probably bad.
Most of the time it is because of a bad slave cylinder that does not hold pressre or is leaking. They use brake fluid and to check them look at the CLUTCH MASTER CYLINDER near the firewall.
On mine, it started leaking fluid onto the carpet behind the pedals. It's are real fix to replace the entire clutch master cylinder. There are also rebuild kits that can save you some $$.
If there is fluid leaking from it in the engine bay in front of your tranny, its bad, also check the master cylinder on the floor board conecting your clutch pedal they can both leak brake fluid. Both are very easy to replace.