When you buy a filter from Porsche the O-ring is in the box, but not the crush washer. The reason is that the filter is used on other vehicles that use different washer(s). You need to ask for the washer. If the parts guy is smart he will ask you what vehicle you have so he can get the correct washer.
Porsche has switch oil filter brands.
I am using a Wix oil filter. I found out about Wix from a guy on the Pelican board who said he bought it from Napa. No Napa where I live, but I was able to find the Wix filter at an independent car parts place down the street from me. I do not know if Napa sells a brand other than Wix.
http://www.renntech.org/forums/index.php?showtopic=9454&hl=unapproved