When I purchased my lovely 2004 CLK from a garage it came with a spare key but did not work, OK I thought it just needs new batteries which I renewed, but still no good, would not lock or unlock the car. I decided to send it off for repair which cost £25.50 on ebay, and parked it at a friends house as the key was not in my possession, and a few days later the key arrived in the post all fully working `great`. I tried to unlock the car and guess what it would not, so I tried it in the ignition (which I never tried before) and it would not even turn. I removed and compaired the key blades with the key that works and its the WRONG DAMED KEY and would fit someone elses Merc but not mine. I phoned the garage where I got the car from with no luck on the right spare key. So if you buy a car and it has more than one key just make sure they are the correct keys for the car. I wonder how much a new spare would be ?