Does the clutch get stuck to the floor and you manually have to bring it back up?
If it's the slave cylinder, the clutch will get stuck to the floor. You'll also have clutch fluid leaking inside the car in the drivers footwell.
Brand new kits (slave cylinder) is like $40 brand new... but that'll last 10 years or so. Get a steel bearing sleeve kit, get that installed and it will outlast the age of the car.
Also, check your clutch fluid reservoir. If it's low or empty, then you have a leak either from the master and/or slave. Best to get both repaired at the same time, as they'll usually give up together.