w/ only 33k on the clock, it's much more likely to be a hydraulic line as already mentioned, or the Master or Slave cylinder. Don't opt for a new clutch before checking these. How long has it been since you changed your brake fluid? Longer than 2 yrs? Then you're due. Heavily moisture-saturated fluid could cause what you're experiencing, but you'd also have a very poor brake pedal feel as well since the Boxster shares the same reservoir for both the brake and clutch fluid.