Quote Originally Posted by psmedley View Post

Next on my list is transmission fluid, as whilst the mileage is low, the fluid is a brown colour.
That's not a good sign. But your plan to do the changes in stages will probably rectify that.

From what I've read so far, about half the fluid is Accessible from the pan via the drain plug. So I figure that if I drain and replace the fluid, do some driving, then repeat, then I should be able to replace around 75% of the fluid relatively cheaply/easily.
About 1/3 of the fluid will be removed. You are correct in that doing partial drain and fill in stages will eventually change all the fluid. I'd recommend doing it initially, then in three months, then again in six month intervals, depending on the resulting color of the fluid.

You might find this thread interesting: click here.

Looking at using a Castro multivehicle fluid -http://productsforyou.castrol.com.au/product/Castrol-Transmax-Multivehicle/35 Can anyone confirm the volume of fluid I should get when draining via the oil pan so I can on firm how much fluid I'll need for 2x drain/fill cycles per above?
IMHO the best value for your money is this product: Valvoline.com > Products > MaxLife > Automatic Transmission Fluid MaxLife > MaxLife® DEX/MERC ATF Buy it by the gallon size. It's T-IV, which is the recommended fluid.
I also assume the only way of refilling fluid is via the trans Dip stick?
That's correct. You will need a small funnel and patience in pouring the fluid in slowly, so as not to slosh it out of the fill tube.