Trans seems to be fine. The oil is becoming more red - I bought 2 extra bottles of TQ95 today. One lot went in this arvo - i'll drive around for a bit before I do another drop and change in a few days.

I hope the oil is compatible with whatever was in there originally.

Castrol TQ95 ... and other 95-spec fluid is red when new.

So TQ95 is the correct fluid? And would it be compatible with other fluid that could have been used in the box?

Gotta do one more flush soon, which should drop the total of old oil statistically down to only 12%

1) Dextron III is compatible with BTR 4spd autos.

2) Tranny oil only changes colour to brown from heat. Could be from a single overheating instance, or a little heat over an extended period of months. Brown oil is old and should be changed asap.

3) The only way to get as much of the old brown oil out is to do a proper flush. That is, where you are draining the tranny oil at the same time as pumping new oil in. Ask your mechanic if in doubt. This will get most the oil out first time every time. If you don't do it properly you'll have old oil left over in the torque convertor for example and it will mix back in with the new oil and that's not the best idea obviously.

So if I were to pump new fluid into the inlet cooling pipe, untill the brown fluid stops coming out, would that work?

You'd need to have the engine running to get the torque converter to turn the pump. What would most likely work is to keep the pan topped up while disconnecting the cooler return line. I'm sure theres more than one path for the oil to flow, so you'd have to ask a transmission place.