They are cheaper on eBay. Just be sure to get the newer one (black plastic housing, not the "chrome" plastic housing). You can install it yourself, it just snaps in. There is a little release button to slide the old phone cradle off the electrical connector in the arm rest. Then the new Bluetooth adapter slides onto the connector. The radio recognizes it automatically. Then hold down the MB logo on the adapter, until it blinks , to put it in discoverable mode. The Bluetooth security key you will have to type into the phone after pairing is 62872 which is "MBUSA".

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech