I think the seals are going on our brake master cylinder, the pedal sinks to the floor under continued pressure. I understand the VRS has a larger piston diameter than the other mk2 Octavias and indeed than the mk5 Golf GTi. Does anyone have the part number for the larger (23.8mm?) brake master cylinder? It's a petrol if that matters. 

 

Is the part shared with any other mk5/mk6 Golf based cars? 

Check out etka.cc

Cheers. Very useful site (assuming it's right).