This post gives an explanation of how the key works for US models and suggests a work around. -- at your own risk!!!! that's assuming your problem is with the key/ignition switch in the first place !!!
Getting another key - Page 7 - Mercedes-Benz Forum
e.g.
The USA SLK key fob consists of three separate components integrated into one package: a mechanical ignition key, a radio frequency (RF) transmitter, and a radio frequency identification (RFID) module.
The flat key consists of the combination of a mechanical key and an RFID imbedded in the plastic head.
The mechanical key is of course cut to match the mechanical lock on the ignition switch. It can be removed and replaced from the fob, so it is possible to alter this portion of the fob to match another vehicle.
The RF transmitter is powered by a battery and activated by the buttons on the remote to lock and unlock the doors and, if so equipped, arm and disarm the alarm. It works much like a garage door opener and uses a rolling code technology. This technology requires that the transmitter and receiver be in synchronization. The receiver must know the next code(s) to expect from the transmitter. Since the owner’s manual describes how to synchronize transmitters, it is reasonable to assume that the RF transmitter portion of a fob bought off eBay could be synchronized to your car (although I have never tried it). Note that when you synchronize it is actually the receiver (the car) that is programmed to or learns the transmitter, not vice versa.
The RFID is a small passive device, meaning it has no power supply of its own. Its main components are a coil, a capacitor, and a chip. These components are typically sealed in glass, cylindrical in shape, and quite small like a grain of rice . Surrounding the SLK ignition switch is a coil. When you turn your key to start your car, the Drive Authorization System (DAS) sends a high-frequency burst to the ignition switch coil. This induces a current in the nearby RFID coil which charges the capacitor. The capacitor in turn powers the chip for a short time. The chip sends back a coded pulse which is now received by the ignition switch coil and relayed back to the DAS. If the DAS likes it, it tells the ECU to start the engine.
The RFID can be programmed once and only once with a code to broadcast. It can be programmed using a special transmitter. It is programmed with a code, or number, that matches the DAS in your car in effect, your VIN. Since it cannot be reprogrammed, it is not possible to use one from a different car to start your car.
Your safest bet as advised is to to get it on a Star machine to identify the source of the problem otherwise if you are not carefull you can start throwing money at imaginary problems.
