Somewhere on the 'Net, on a Porsche forum site, a gentleman posted an illustrated seal replacement for his NipponDenso compressor, very similar to our compressor. As I recall, it was not bad to do. If I run across the site I will post.
One link: http://www.pelicanparts.com/techarticles/911_Nippondenso_rebuild/911_Nippondenso_rebuild.htm