Figuring out oil leak in Boxster S

[vkmotorsports]

Hello
In my 2001 Boxster S, there looks to be an oil leak here as seen in the picture attached.

1) How can I go about diagnosing it myself ?

2) Is this a valve cover gasket leak ? How can I confirm that ?

3) Is there some other leak that is possible here ? The oil levels do not drop while driving or over time. Maybe after 3 months of driving or say 500 miles, I add a 100 - 150 ml of oil to the engine.

Please help/advise.

Thanks in advance.

VK