Depending on the mileage it is probably either the spark plug tubes, the variocam solenoid, or the cam cover itself.
Here are a few links to tech content that will help you see what I am talking about
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Here is the Spark Plug replacement, which includes the coil removal
Porsche 911 Carrera Spark Plug Replacement - 996 (1998-2005) - 997 (2005-2012) - Pelican Parts Technical Article
Youll see the spark plug tubes in figure 6, these can be replaced by removing the coils and spark plugs...cam cover can stay in place.
Porsche 911 Carrera Camshaft Swap and Valve Train Repair - 996 (1998-2005) - 997 (2005-2012) - Pelican Parts Technical Article
Could also be leaking from a bolt, you just have to look and see. Let me know what you find!