I had a garage examine it again, they said the coolant housing at the cylinder head needs to be replaced. However when I examine that housing myself (looks like a plastic part at the side of the engine) I don't see any evidence of a coolant drip. Would I expect to see some white residue there? I don't have any other testing equipment.
To hopefully make it easier to see, today I just washed down that whole area and am hoping that a leak will be visible, but no signs yet.