Frodo,
It's hard difficult to say that it's safe to drive the car with a bad AOS. This will depend on how bad the leak is and if it's affecting the way the nine is running. Do you have ny CEL codes? As Jäger mentioned most of us that have had AOS that have failed didn't know it untill it was already a large leak. Best advise is to have it replaced sooner than later and ont drive it untill it's been repaired. I had my failure just 6 months into ownership and didn't even know how to access the engine. Than I found this DIY bt Brad
http://986forum.com/forums/general-discussions/18090-air-oil-seperator-write-up-5.html this used to have pictures but seems its no longer available.
I do have one tip in doing this. Most new AOS comes ith a new lower hose. The clamps that hold the hose are difficult to reach. Don't bother trying to loosen the clamp for this hose. Just cut the hose using a knife but with care o you don't damage anything else in there.
Hope this helps
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