2011 SRI diesel auto gearbox

[Jimsharp39]

Afternoon, now about 12000 miles into ownership and have to say how surprised at how generally good this car has been. I was expecting it to be rubbish, but has turned out a reliable mile muncher.
Can anyone with access to to a parts catalogue oblige with a part number for the drain plug washer for the six speed auto fitted to my 2011 sri cdti?
I have had a search but couldnt find anything.
Cheers

Jim