Important – Special Oil Requirements "To benefit from the new technology and Audi Variable Service Intervals, newly developed Long Life oils such as Castrol SLX OW30 Long Life 2 must be used (please refer to owners handbook). They have been specially formulated for Audi and are a new generation of ultra high-grade synthetic oils designed to withstand ageing and high loads without deterioration. Using ordinary high quality multigrade oil will not cause any engine damage but it will defeat the object of the new technology and cause a service to be needed at 10,000 miles. In addition, compared with conventional oils, Long Life oils gives exceptional levels of engine protection, are kinder to the environment and deliver fuel savings. In recent tests carried out on vehicles in Germany SLX Long Life 2 resulted in a fuel saving of 2.72%" An explaination of Variable Service..up to 19,000 miles. http://www.audi.co.uk/customer/servicingoption.jsp For me, GC is the way to go.