I too have an s320, but I have never had the problems you describe. From your writeup, it sounds like you either have a small oil leak getting on the exhause manifold or your mechanic spilled oil or grease onto a hot engine surface. Either way, you need to find a new mechanic for future work. That kind of sloppiness (not to mention not closing your hood completely) could easily be aprecursor of a botched repair job. I would watch this very closely for a few days, checking my oil and fluids as often as possible. If it is just spilled oil or grease, it will burn off and stop. If it is a leak, it will continue and probably get worse.

Good luck,

__________________
KCScout
98 S420 My Wife's Baby
97 S320 My road car
83 300D My old road car (love that diesel)
81 300SD Wife's former Baby
81 240D A fun stick shifter
71 220D My first one