I recall a while back there was some discussion about whether to go synthetic or not and what brand one should use. Recently, a couple people on vwvortex.com had both mobil 1 0w-40 and amsoil 5w-30 analyzed. The results were that the Mobil 1 held up pretty well at a 5000 mile drain interval. The amsoil, on the other hand, was beginning to go at 5200 miles. Interesting that amsoil advertises long drain intervals as one of its cost justifications but it seemed to be breaking down at 5200 miles in a stock Volkswagen 1.8t engine. The guy who analyzed the mobil 1 was running a "chipped" (modified for more performance) and drove harder than the guy with the amsoil. Yet, even in the modified engine, the Mobil 1 held up better.