If memory serves me the valet key was round where your hold it not 'squarish'. I had a new ignition lock a few years back installed on my ML55 and it came from the factory with a key...but it of course doesn't work to start the engine as it doesn't have a transponder. I seem to think the red dot on the key was only in the 80's and was deleted later on - even on replacement keys.

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1988 Mercedes-Benz 300E 5 Speed ~200k
1958 Mercedes-Benz 190SL (sold)
2000 Mercedes-Benz ML55 AMG ~230k - FOR SALE
2003 Audi A4 1.8T Quattro - Wife's Car
2007 GL450