Most of the time on this engine when the belt is making noise only the shock is bad. The rubber bushings in the shock get play and make a rattling type noise. I have seen lower control arm bushings go bad well before 60k miles.The labor they are telling you for repairs is resonable.This is not a DIY job.Requires special tools and alignment after replacing bushings. The labor they want for the door check straps seems high.
Mercedes Benz Master Tech