Hello,
Try this: park on flat ground, handbrake off, out of gear.
Pump up the brakes hard, hold down the pedal and then switch off.
You should feel the pedal rise slightly.
If not above then start looking at quality of flexibles, and one way valve. Do this with engine running and look to see if any hoses collapse under vacuum.
Servos are very reliable, do remember to change the brake fluid regularly,(with time it absorbs water), which can cause brakes to lock up when hot.
Cordialement,
