I just purchased a 2004 A4 1.8T, quattro 6 spd. manual with 137k. The previous owner maintained it well and had receipts of major service work completed in the last 15k miles including timing belt, water pump etc. It's due for an oil change and I'm wondering what the intervals should be with this mileage. Also, he said he used castrol gtx high mileage oil. Should I continue to use this or use synthetic? If all goes well, to what mileage will these cars go until? I've never owned a foreign car so I need to become educated on these a4's. Thanks for everyone's help and insight!