£2.4k by a specialist, and warranty won't cover it as classed as wear and tear, even though part of an auto box.
With Audi warranty I imagine though they'd say it's a new box, as they wouldn't take the box apart to diagnose it properly, and given the fact they wouldn't cover your prior repair I doubt they'd cover a £10k box, especially given the not in time oil change.
This is just a guess though so it could be a faulty unit they put in, or could be something else.
Audi said the selector levers were getting resistance and non serviceable so new box, but specialist replaced clutches that they found to be burnt and had no errors since and engages reverse straight away.
Either way whatever their diagnosis, I'd want my money back for the repair they've just done as sounds like it was the wrong repair, with an upside you've just got a new mech unit, plus a refund on your warranty