Depends on where you live.

The USA recommended interval is 13K miles and there's NOTHING to recommend changing it more often.

Car should have a maintenance manual in addition to the operators manual and you can get one from a dealer. Or, join owners online at mbusa.com and download one.

BTW, you must use synthetic oil to MB spec 229.5.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles