well, here is the damage,
Apparantly the first drum is known as a weak spot such that the supplier won't even guarantee them to the garage, he has had to cover the whole job and his view is that they can and do go regularly on this model of box as it is the main thing he see's A8s in for
The drum actually splits and then the clutch plates come loose. this allows the piston to move and the seal then breaks.
Pictures
