I could be wrong but from what I have researched, the indents on those pistons are factory. The portion of the piston where the carbon was rubbed off is where the valves hit. If you google 2004 chevy aveo piston, you can find an image of a factory new piston with those marks. My only guess is they were placed in the pistons to add clearance for the valves. Do you still think the motor is done if those marks are factory?