This happened to miggy at about 75,000mls
had a slight stall when moveing away from traffic lights
I read the stored code and now can't recall what it was
Anyhow under advice from TB

I changed the ATF and filter etc a few weeks later
Still used miggy for a hundred or so mls
My impression since is it was the autobox asking for a service
30,000mls later (many of those mls tugging a caravan) miggy has a box smooth as silk with no problems
As Albs advises I most certainly would NOT use that additive as you will contaminate the total fluid content of box and fluid flywheel
And I don't think it's possible ever to drain out all the fluid only about 50%
There are lots of guy's more qualified than I on here (with better memories)
I just felt I needed to add my thought's and a cautionary note with regard to the additve
Best of luck Nick,hope you get it sorted OK
