i would say keep the car running on the same oil if it aint creating problems.
ur car should do 16-17km/l in summers with AC. If it does not fill it up with 50% hioctane and 50% regular in a full tank of gas.
as far as gear oil goes. do see ur car's dip stick. it should tell u to use a specific oil.
i added moly's ceratec to my 2010 alto n got moly oil but after doin it i thought ytf did i spend so much on a small car.
i used to get toyota petron plus with toyota genuine thai made oil filter for my car n the cost was 2500.
with moly products mentioned above i spent 7000 on fluids and 700 on filter. which i thin wont be worth the money.