New clutch master cylinder, for the clutch pedal, on VW MkV Jetta and Mk6 Jetta, Golf and Sportwagen with the 5-speed or 6-speed manual transmission. Has built in clutch interlock sensor/switch.
If your Mk5 Jetta does not crank from time to time the sensor in the slave may be failing.
VW has updated the design of the clutch hydraulic line and a new line may be needed for installing the master and slave cylinder.