What I've found on most of the Boxsters that leaked oil near the head is that the spark plug tube o-rings needed to be replaced.
Here's a thread with some discussion and details:
Spark plug tubes
Here's how the leak looked on my current project:
It's not very difficult to DIY, parts are cheap, and it is a great time to change the spark plugs as well. This is a very common problem on 1997 - 2002 cars. Later cars have metal tubes integrated into the cover.
There are other things that leak, but this is what I'd look at first. Leaks from the mating surface of the cover are pretty rare.