I think you need to first establish whether or not the smell is actually coolant (it's scent should be distinctive enough). If it is, then you have done all the right steps to nail down or eliminate the possibilities. But the fact remains that if you are *really* smelling ethylene glycol, there has to be a leak somewhere. It may be a teeny tiny pinhole leak, and may be functionally OK for now (i.e. no measureable coolant loss), but fall in the category of unacceptible aethstically. And eventually the leak will get worse.

Are you sure it's not coming from under the hood somewhere (water pump freeze plug, radiator connection, etc.)? I had a pinhole leak in my plastic overflow tank, which was only visible with the soap test.

Gerald C