Just a reminder

Mercedes of that era came with two keys, a master, and a valet key. Both worked in the ignition and doors and you could start the car with both of them, but the valet key would not open the glove box or trunk.

If your trunk key unlocks the glove box and doors, but wont turn the ignition, either the ignition tumbler has been changed or it is damaged, and I do not believe you can order a lock cylinder keyed as original to the VIN.

If the key your working in the trunk does NOT open the doors or glovebox, my bet is the trunk lock was changed and you might get lucky ordering a Master key off the VIN.

If not, you have a lot of work ahead of you.