I think you would likely have to replace the unit for a newer unit with the later firmware installed.??Not all consumer devices can have the firmware upgraded after manufacturing, it maybe that they would have to mount the internal PCB on a rig to write to it and there is no external writing method.??You also have to tkae into account that some of the circuitry or at least components may have changed inside which is what warranted a different firmware revision in the first place.
I don't think you have much of a leg to stand on as it will meet the original specifications of when the car was sold.??That being said, best of luck.