Holden Cruze 2016: Slipping automatic transmission

I bought a new 2016 Holden Cruze Z, the last of the models built at the Elizabeth plant. My problem is that the automatic transmission oil is not clean or clear red to pink which would be expected in a new car, it is blacker than black. The transmission seems to slip or flare under acceleration without increase in vehicle speed since new. Now, just this week the engine seems to be at 2500rpm at 60 km/h, but it doesn’t happen all the time. I have brought this to the attention of Holden during regular servicing as per their recommended service book, but they say they didn't pick it up on a test run. In the two years since I have had the car from new, it has done only 16,857 km and has not been thrashed. Knowing something was amiss I had an independent auto transmission specialist look at the car and they reported the transmission oil is very bad. The oil is blacker than black, as the man said he would have expected this on a vehicle if it had done 100,000 km or more. I have also booked the car into another place for a second opinion I have confronted the Holden dealership where I bought the car and I requested they fix this under warranty, but they said they want the car all the day it is booked in for. Should I have to pay for them to diagnose what is wrong? Should I ask them to replace the auto transmission, it seems to me the transmission oil should last far longer than it has so far? What should I expect now?