Today I tried to put a HG cassette on a Dura Ace FH-7403hub, which has a HG/UG compatible body. Since I bought my wheelset on the Internet, I didn't notice the hub had been put together incorrect, so while trying to fit the locknut for the HG cassette, a small ring inside the body broke apart as it was mounted the wrong way around .... It is marked as nr. 13 in the picture below.
Can I get such a ring at my Shimano dealer? Of does anyone have one lying around?