Looking at my next oil change for the S4, I usually use f/synth 5w40 VW spec oil (502.00/505.00). I can get a fairly good deal on Mobil Super 3000 X1 5w40 (£28 for 5 litres) - is it likely to be any better than the other VW spec oils, or are they all the same?
Mobil oils always seem thinner than others, and every time I've used Mobil it's always been burnt by the engine that otherwise didn't burn oil from Fuchs.