Correct gear oil is 75w-90 , which has drain interval of 15000KM.
i got it changed on 17000km and there was some metallic residue.
Normaly dealership asks to use GL4, but i wanted the same oil coming from factory which is not available on every dealership but they can arrange, cost around 8000 for 2 liters, however GL4 cost 2000 for 2 liters.
the manual gear box takes 2.3 liters.
i feel almost no difference is gear operation and fuel consumption also same as before.
in short, if you use 75w-90 then drain internal is 15000KM
if you use GL4 then it can be used for 30000kms