I've noticed that my brake vacuum assist fails, but not all that often, I suspect there's a blokage in the hard plastic pipe from the manifold. I thought I should change this pipe but not any pipe will do by the looks of the material it's made of. As you know, this pipe is quite hard. I suppose this is so it won't collaps under vaccum. Does anyone know how I should go about removing and replacing this and with what type of plastic? I can't seem to find the correct fitting off the shelf.Regards. John