Gearbox & transmission oils

After reading a feature in CM regarding gearbox oil changes, I have decided to perform one on my 2011 Audi A4 Avant 2-litre TDI 170, the Quattro version with a six-speed manual transmission. The mileage is currently 70,000. However, I cannot find the gearbox oil specifications or quantities. I am also looking to change the rear transmission oil and again cannot find specifications or quantities. I would like to use a good quality brand such as Castrol. Simon Devlin

The gearbox oil capacity is 4.5 litres and the rear diff capacity is 0.9 litres. The genuine part number of the oil is G052911A. Castrol Syntrax Long Life 75w90 would be perfect for the job.