'02 Merc S320 diesel. Merc are saying that a cat needs replaced because 'there's a small amout of soot between the turbo and the flame catcher (sic.), so we think there's an air leak somewhere'. Given a separate, independent merc specialist has said 'there's nowt wrong with it guv', I would appreciate what the combined millennia of relevant experience in this group have to say on such evidence, the cause and the work required.
The car appears to run perfectly.
TIA
Chandy