Rear locking Diff oil to change or not?

[Robbouchard]

I am running a 2012 LR4, 144,000km. I have a question regarding whether or not to change the oil in the rear locking diff and transfer box. The manual states it needs changing at 120,000 km. My local LR dealer performed this service and did not change the oil. When I called to check why, they said they checked it and it was clean and levels were good so they didn’t change it. When I took it to an after market guy for the 144,000 km service he is recommending it be changed as per the maintenance schedule. He comes recommended but is he just trying to push this on me? Can you tell when oil is good or not? Should I just get it changed? I do not do any off-road driving to speak of but do tow a 27ft travel trailer.