I recently bought Altis 1.6 2015 Auto and the dealership told me the same thing when i went to change the gear oil and they said they wont change it becuase oil was so black and burnt. Then I spoke their manager and he took a test drive and gear was working and then they agree to change the oil and the guy did a really good job.
They also made me sign a paper incase if something goes wrong, they wont be responsible. I signed it.
After changing the oil, they let the car run for 1 hour on idle and then took a test drive again to check if sensors were working fine and gears were shifting. Alhumdillah it went well.
Make sure to change gear oil filter and gasket too. Dealership will take care of everything.You may buy gear oil filter from outside (buy only original). I bought is from a local shop and saved 10K. Dealership was selling gear oil filter for 19K. I bougth the same for 10K from local shop. Buy the oil from dealership
DON'T GET IT CHANGED FROM A LOCAL MECHINIC. ONLY GET IT DONE FROM THE DEALERSHIP.
Let me know how it goes. Best of luck