Assuming this is the AW-55 5 Speed gearbox, then it is not a simple complete drain and fill, it has to be done in parts. Eventually, once the oil is nice and red, you may have to complete gearbox reset with VIDA, so that you tell it that the gearbox oil is refreshed.
From my side, it takes about 4 attempts at 3litres each time.
Use the yellow dipstick though at the end and shift through the gears each time. I played it safe and drove the car for about a week between each fluid change.
__________________
|