There are a few choices here, the non parking brake drum area of the shield can be straightened, the area under the parking brake shoes is complicated and difficult to straighten so not much damage here will warrant replacement.

The hub will need to be pressed out of the bearing to change the shield , this will destroy the bearing. A more direct and home garage friendly route is to purchase a complete used hub carrier that will include the hub , bearing, dust shield, parking brake shoes / hardware.

Removal of the rear hub nut requires the locking tab to be bent back and substantial torque to be applied. Given your questions, this repair might be beyond your tools / resources. If you took it to a shop, ~ 1 1/2 hr should cover a complete hub carrier replacement.

Go to car-part.com enter 2003 C320 , your metro area then look under " rear axle, stub only " This brings up many parts ranging from $ 300 at the " I think it is gold " to the $ 100 " this is what it is worth because it is a slow mover " yards to the $ 50 I'll sell at a good price to move material.