have they said its the dephaser pulley at fault - that its started to break up inside ?
might be a chance to remove the head and flush all the swarf out and rebuild - its better being alli than steel swarf!
That is a good point, the technicians there are very good from my experience and i am confident from what i saw yesterday and the way they are working around the car they will get to the bottom of what it is and provide the cheapest proper solution that they can.