Where do you top up a automatic gearbox on a volkswagen transporter t4?

In my experience with these things, having owned one from 2000 to 2006 and covering only 150 odd thousand miles from new. The gearbox is a sealed unit and seemingly needs to be replaced every 40,000 miles at great expense. Joking aside, specialist tools are required to top up the oil as the quantity is reliant on the temprature of the unit which alters the volume of oil and the oil is locked in at a certain temp and the selector lever has to be moved in a specific mannor to distribute the oil around the valve block, also the bands need to be tightend every so often.