If the amount of coolant lost is slight or negligible, it doesn’t pay to worry over it. My Aveo is too new to have this problem, but other cars I had have had slight leaks. One could only be smelled under the hood when the motor was hot. That was probably a leak at the head gasket, and it would lose a few ounces per month. Another car I have drips a few drops of coolant only when parked overnight in my garage – I can’t find where it is coming from at all. Another car of mine has a smell of coolant through the vents in the cabin only for the first ten minutes after startup – that’s probably in the heater core. These sort of things are not worth losing sleep over. Just keep an eye the coolant level monthly to be safe.