how does the key ingition come out???????, i need to replace.......

With some difficulty. 1) Disconnect your battery and make sure your front wheels are pointing forward and your steering wheel is straight. using a small flat blade screw driver, pop the mercedes emblem out of the centre of the steering wheel and undo the 10mm allen bolt holding the wheel to the steering column. At this point it may be useful BEFORE you pull the wheel off, to mark the position of the wheel on the splines with a black marker to make sure you put it back on in exactly the right position. 2) Now the steering wheel's out of the way you can pull the instrument cluster out. You'll need a long thin metal hook (put a wire coat hanger in a vice and bend the end into a hook about 4mm long), slide the hook between the edge of the plasic and the leather of the dash and turn it so the hook catches on the back of the instruments (don't worry you won't damage it) and pull the cluster forwards, it may be a bit tight if they've never been out before but just keep pulling and they'll come eventually. Once you've got the cluster out unscrew the speedo cable and remove all the other leads noting the position of each one. 3) Looking into the hole where the instruments used to be in the direction of the ignition you'll see where the ignition barrel connects to the steering column. Undo the 10mm bolt which is clamping it. where you put the key into the ignition, pop the pastic ring off the dash. Go back now to where the instruments used to be and look just inside the hole. You should see 2 more bolts holding the steering column up to a cross member, take them out so the column drops down a little. Put the key into the ignition. Reach through the instrument hole for the plug on the back of the ignition barrel and pull it off whilst turning the key until you feel the plug budge. Finally the ignition barrel should just slide out of the column with a bit of wiggling. Hope this is helpful and if anyone reading this answer thinks i've missed a step then feel free to correct me (it's been 5 years since i've done one of these so memory's a bit rusty)