Good news, i took the van back to the dealer to diagnose the erratic gearbox downshift, and whilst they were unable to replicate the fault or find any fault codes, they did locate a tech bulletin which describes the exact same issue and were able to apply a fix in the form of a software update.

Whilst i'm hugely disappointed with the premature failure of the gearbox and the lack of explanation from VW Australia, i have nothing but praise for the local dealership who has been very helpful and accommodating through the whole process.

On a side note, is there an online repository of all tech bulletins?