smoke coming from engine compartment?

Hello to everyone,
I had some preventive maint. done to my newly acquired 79 300cd. i.e, oil change, fuel filters, adjusted the valves, air filter etc. I also had the old smudge and old oil steamed off the engine. After I get the car back home I notice that I have smoke coming from around the manifold/bottom,air filter compartment area. At first I thought it was just oil had gotten on the manifold, but after three days it's still smoking in this area. It was not smoking before I had my mechanic do the service. What could be the culprit? Could the manifold be still burning off? I'm getting worried and really need some advice. I don't want to mess up this really nice machine. Please help. Thanks to all in advance.