[CL9] Changing Automatic Transmission Fluid

[seanneko]

I change Auto fluid every 20,000km, if you consider when you drain the Auto fluid you only drain a little over 1/3 of the total capacity (2.5lts to refill, total capacity is just over 6 lts). In theory that means your changing the full capacity of the transmission every 60,000km, but in reality it doesn't work that way as your always mixing new oil with old.

Couple of questions...

The CL9 service book says that auto transmission fluid is changed every 120,000km. Do they do a full flush of the entire thing, or just replace the 2.8 litres that drains from it? If it's the latter, isn't this bad, since essentially the car will always have old fluid.

Also, how sensitive is the transmission to the level of fluid? I remember on my old Statesman you absolutely had to get the right amount in. Too much or too little would make it slip, hold gears too long, etc.

Is it true that you have to use genuine Honda fluid rather than a generic one from SCA, Autobarn etc? If so, can you get it anywhere except dealers? Can't seem to find any on ebay...