Long story short, VW have made changing the oil on the 02S gearbox much more difficult than on the 02J and it’s critical not to make a mistake or the box will be under filled which could starve the diff of oil.
In short, here is what you need to know.
Oil needs to measured when you take it out.
And it should be refilled through the reverse switch hole. According to VW. Here is a link to the procedure.