190E trunk lock actuator

[kiato4]

Hey all:
My trunk locks and unlocks when the car is opened from the front doors, but if I lock or unlock the car from the trunk only the trunk is affected and the rest of the central locking system does not work. I suspected a bad actuator so I ordered a new one. It seems that the updated part is 124-800-16-75, but the mounting holes are different than on my car and it looks different. The Mercedes dealer swears this is the right part, as does performance products and fastlane. How can the mounting holes be different than the holes on the trunk lid? Does the actuator mount to the plastic casing inside the trunk lid that surrounds it or directly to the trunk? Thanks in advance.