This video shows the steps to replace the crankcase vent valve on a Porsche Boxster 986. The vent is part of the Air Oil Separator system and it functions to relieve over pressure in the system. It has been speculated that if this vent goes bad, it will cause failure of the Air Oil Separator.

A full step by step guide and tool list can be found at ZipZapDIY.com: Boxster Crankcase Vent Replacement