Hi I need some guidance looking to buy 06/07 A6 diesel preferably automatic but can someone tell me what service and when does an auto gear box need and what other problems to look out for and info much appreciated thanks. 

My advice would be to get a quattro auto (Tiptronic), they are sealed for life and have no need to be serviced, plus they are less prone to problems. The front wheel drive options came with a multitronic box which was much more prone to issues. The service for the multitronic box should be a gearbox oil change every 40,000 miles. Hope this helps.