I've had another look today and cleaned round, the main area is drivers side to rear where the diff bolts on. I've got it booked In on Saturday to get the gasket changed and the gearbox service, but I've spoke to a gearbox specialist who's said leave it and monitor it as the pan gasket will be changed on its service anyway. That's another 10k though, not sure I'm confident enough to leave it that long.
Today I also emailed audi customer service and basically asked them if they would investigate the leak free of charge as although it's out of warranty by 6 month, it's still 30k miles under what there warranty covers. If it's a failed gasket at 28k, to me that's a manufacturing fault. Not hoping on this like, but it's worth a try...