What oil is used in a 2001 Audi A 4 1.8t?

Audi sent a bulletin to owners changing the spec to a VW approved full synthetic, 5w40 preferred or 5w30 acceptable. I never bothered to investigate VW spec. I've used Mobil 1 5w30 since 30k. I have 110,000 miles now and still going strong. I change oil more often than the 10K spec, more like 6-7k. I've read several posts about oil sludge and various probllems with A4 1.8Ts. Maybe just good luck but this is the most reliable car I've ever owned. I'm betting frequent oil changes with full synthetic are really important for this model.