Brake Shudder

Hi, I have a 2008 phaeton and have experienced brake Shudder...
I have replaced disc and pads which cured the problem for around 3K miles.
I have since changed discs and pads 4 times and tried different manufacturers.
I've even changed the front and rear front suspension arms and bushes.
The hubs have been checked and reported as true... Any ideas pls....
The car now has 117000 mls is that a lot for a 3ltr turbo diesel engine??? I previously had a Mercedes S class and that started to give trouble at 106000, gearbox gave up...This Vw has been the best car I've ever owned so I hope I can cure this and hold on to it for now. I should add the Shudder is only there just now above 50mph...
Cheers
Paul