i'm doing this same job now on mine. i have the thing off the car and in my case the key won't turn one bit so there is now way to get the tumbler off. it would stick avery now and then but now it won't move at all. i'm takning the assembly toa locksmith tomorrow and see if he can fix the thing. if not ... i guess it's the dealer. btw the thing has mercedes benz written on it. and the only numbers are 2020 YMOS. will post when i know more.