rock chuck is correct in saying slave cylinder, not master, (I'm on some heavy duty pain stuff right now so my brain is not all with it)
But anyhow when the slave starts failing you will see brake fluid leaking under the trans or you will notice the master cylinder resevor getting low, when it fails or you are out of fluid the clutch peddle will stay on the floor with the clutch disengaged, there is not anything you can really due to prevent it from happening. With the head gaskets start the truck while it is running pull of the radiator cap or just look in the coolant tank and see if there are bubbles when the truck is running, also check the oil to see if there is any coolant in the oil, and check for white smoke out of the exhaust, when it is cold you will have the condensation steam but after it has warmed up if you are "burning coolant" you will know.
