Transmission FLuid

[DRW1000]

You're correct. However that is better than not changing it.

[Kevcules]

You don't even get 50%, more like 30%. A regular fluid change refill is about 4 litres. Most vehicles hold 10 to 12 litres. A complete flush is best but not common.

[DRW1000]

There is some debate about flushing too. Some machines flush in the direction of flow and others against it there are debates about harm from pressure from external pressures. I have had one dealer tell me one way is best and not to do the other and another dealer tell me the exact opposite.

I just think you are better replacing some (I think it is close to 50%) then none at all and it you do it twice within a week or so then you have changed 75% (assuming 50 % each time).