My Chevrolet dealer told me that engine damage claims due to oil (which never happen lol) would not be covered with amsoil non-api approved synthetics, which are there 25k and 35k mile oils. There information on the oil states that Amsoil synthetics use a level of ZDDP that is much to high to be approved by the API, and in result can damage a catalytic converter.
This is partially bogus, because in order for it to damage the cat converter, the engine would have to be burning oil, and it would take an extrememly long time to do any damage.
In short, i would use the Amsoil and dont worry about it. You will never have to make an engine oil related claim, and all other warrantee services will not be effected. No ones going to know what oil you have in your ecotec, lets be serious.
Also, dont different climate states have different viscosity filler caps on the ecotecs?? Example: dont cavaliers that are shipped to florida get the 10w-30 recommendation, and the new york shipped cavaliers get the 5w-30 recommendation? Either way, a 5w-30 amsoil down in florida will do fine.