2004 Chevy Aveo oil in spark plug well

either your piston rings are worn and will need to be replaced or your valve seals are deteriorated and letting oil leak in.

I know that some of these cars have had problems with the valve guide seals. Is there a misfire or an engine light code? I don't know if this is a warrantied repair unless you have an extended warranty. Otherwise, it's an expensive fix. It wouldn't hurt checking it out.