Background:
In deed, breaking in differential gears is necessary. In the beginning the surfaces are not aligned to each other. Small uneven edges and peaks have remained from the mechanical treatment. That impedes heat transfer between the gears and its teeth. In addition the metal structure is not as dense at that time as after breaking in.
That's why in the beginning you should not tow, require high torque or drive at high speed. Otherwise you get local overheating and the metal structure is not as dense yet as it should be. That supports breaking out of parts. When the gears harmonize the surfaces getting smoother and their surfaces gain more contact, the structure gets more dense and the heat transfer gets better and to the required level. The oil change is needed to get rid of small metal and attrited phosphatic coating parts.
Maybe this guideline wasn't followed and the damage would have come anyway, having done an oil change or not. Of course, when you would have done the missed oil change the damage which (may have) build up would not have been detected, as no one looks at the gears (except bigger metal parts would have been found in the oil) or the oil would have been analyzed. But it gave Ineos the possibility to reject warranty.
AWo
