I would check the MBUSA website to be certain about feature differences, but for my money, I'd get the deal.
In 2001 they updated the EMS and traction control. In 2002 they added missing niceties like climate control, one touch window switches, head protection air bags (lost the power roof though

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In 2003, you have the ML500.... get a 2002 320 at $500 over invoice and you'll be happiest!