Since there are no replies, I'll reply to my own question - the standard answer from Auto Bavaria (it's a Malaysian car) is 100,000km. HOWEVER, I just had the gearbox oil drained at 80,000km and it is B L A C K and full of sediments. No wonder the gearbox was not shifting smoothly into 2nd.
The gearbox oil is different from the 6 speed autobox to the 5 speed (and don't believe your mechanic when he says it's the same - apparently they are different grade of oil - I need to flush my gearbox again and fill with the correct oil) and the gearbox oil filter is rather expensive now... compared to previous.
I wouldn't leave my gearbox oil change to 100k km, probably 30k or 40k intervals.