This part is inexpensive : 996 107 047 51
Connection Piece for Oil Separator Vent Line 99610704751 - Genuine Porsche - 996-107-047-51 | Pelican Parts
BUT it is very tedious to replace. Cleaning it may be foolish because of the R&R issues.
1. We really need a Test Method to determine if it is malfunctioning.
2. The later open valve 996-107-047-00 - is it considered an upgrade/substitute for pre-2003 cars ?
http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search_2016.cgi?command=DWsearch&description=vent+line+valve
3.We also need to decide on the while-you-are-in-there list .As Gilles mentions- the Accordian hoses or their O rings are also problematic.
http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search_2016.cgi?command=DWsearch&description=vent+line+hose+AOS