VW master cylinder. We only carry original equipment quality, direct fit master cylinders; you don't ever want to skimp out on brake components. The master cylinder is responsible for converting your foot pressure into stopping power for your vehicle. If your brakes feel spongy, or the pedal is progressively getting softer it is time to replace your master cylinder, before your car no longer stops at all.
When you replace the VW master cylinder you may want to use a new brake fluid reservoir for your Golf or Jetta. This will make sure you don't contaminate your new fluid. Flush fresh brake fluid through your brake lines when you change the master cylinder. Never try to reuse old fluid; over time it draws moisture from the air and then it can't handle the heat generated while stopping.