There is no door. If you had this problem, you will need to replace the tumbler. This is very easy to do for a tech with the right tools IF the tumbler will turn. At my shop, we will install a LOANER tumbler and order the correct one for your key.
IF the tumbler locks up, you will have to pay 5-6 hours labor to have it cut out. That "light alloy cover" is made out of a metal harder than titanium! You will not remove it without c4. And if you do, please tell me how you did.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS