Thanks, Beer.
The german translation for this part is "Ölabscheider".
If this part is broken, the engine will burn much oil in general, not only sometimes. And you will allways have a lot of oil smoke from the exhaust.
There is a description on pelicanparts:
Pelican Technical Article: Boxster Air / Oil Separator Replacement - 986 / 987
There are differences over the years. Attached photo shows a 1997 AOS. Part number is 99610702351. Part number stands on the side of the AOS.
Regards
Markus