I have an 03 E320 and I run 15000 mile OCIs with no problems -- good wear metals and good TBN. MB has changed their OCIs to 13000 miles for non-AMG engines and 10000 miles for AMG's.
Draw a small sample and have a UOA. In a week, you'll know whether or not you can go further! My feeling is the M1 in your MB can go to around 15K from my experience.