https://www.ebay.co.uk/sch/i.html?_f...21113&_sacat=0
You need to replace this, it is beside the gearbox inline with the coolant hoses. Taking off the wheel makes it easier. Might be easier to buy one and get a fast fit place fit it, it is easy enough but almost in the middle of the car is difficult when laid on the floor.. It is just undertrays, two spring clips and some spare coolant to top up. I went with a FEBI one and it has lasted longer than the original VW/Audi one.
I don't know who supplies them but they are a common failure across many VAG models.