I have a run out model (2007 on a '56 plate) C5 2.0HDi Exclusive auto with literally all the bells and whistles which I adore. Two weeks after passing it's recent MOT it suddenly lost power and now pulls like an out of breath sparrow, doing 0-60 eventually if at all. The strange thing is it starts and runs fine, burns no oil, emits no smoke and has no warning lights up. My mechanic diagnosed a seized turbo. Is he right??