Loud hissing from rear of Brake Servo

Car is a 2003 1.0e K12 manual.

There is a loud hissing coming from the brake pedal area inside the car. Cannot be heard from the engine bay.

When you press the brake pedal the noise goes away and the engine revs reduce to normal.

I'm presuming a replacement servo is required but before I bite the bullet, has anyone else had this and if so, was is a new servo jobby? If so, are all the servos the same or are they engine specific?

Cars done 70k. Never known this on any of the K11's I've had. It'll be the last K12 I deal with.

Thanks in advance.
 
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