I am missing the key that goes inside of the (key)fob to a 2003 Mercedes C230. My question is: Can I just replace the metal key that is missing, that goes inside of the housing of a (key)fob, or am I going to have to replace the whole set and where and how can I get this done?
There are a few different styles especially with aftermarket ones but the insert is just an emergency key to unlock door and trunk when the car or fobs battery is dead. There is no problems in replacing this. Not many locksmiths do benz but try around a few in your area and also try getting a quote from Mercedes. Tell them you just need your Emergency key and tell them if you have the old black style fob or the newer chrome version.
Mercedes may not carry the ones for the old black fobs anymore and may try and tell you that you must buy a whole new fob (which is not true, you can still go to a locksmith)
If you have the black style you may also consider getting a whole new case for it online. It will come with an uncut emergency key usually.