Thank you all for the helpful advice!
The car is a manual transmission (sorry should have said this in the initial post!). I bought the car at 135k miles from a company car driver (motorway miles, sales rep stuff etc) so it's generally not been too bashed around town etc. Service history was regular and with Audi main dealers before I bought it and switched to independents for servicing. My mileage is also fairly high so keen to keep the car well looked after and running well for the next 2-3 years until around 180-200k. The engine is very quiet and smooth for a diesel and seems to be running well so fingers crossed! Keen to hear any other maintenance tips for a high mileage vehicle such as this aside from the usual diligent servicing and oil changes.
I will take your advice and call the Audi dealer who serviced it to ask whether they changed the fluid and contact my local independent to take a look.
Thanks again
Rob