The 02 M Class was the last year to use the CD-Rom based nav systems (that require 9 different regional discs depending on your location). In 2003 they were updated to a DVD based system, requiring only one nationwide disc. I would assume you could buy all of the necessary components to convert your system to DVD, but it is probably quite expensive. There may be newer CD versions for your current system (check the dealer first, or eBay sometimes), but they are probably just updated and I would doubt they are any more detailed. I personally don't know of any non-MB databases or upgrades.

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1994 S500 coupe
2005 ML500
2007 E350
(en route) 2005 CL500