The way an automotive shop would locate the leak is by removing the radiator cap and attaching an adapter that screws on in place of the radiator cap. Something that looks like a bicycle pump with a pressure gauge attached to it is used to "pump up" pressure to simulate pressure generated when the cooling system is at operating temperature, the leak is then found sometimes it is obviously leaking from a coolant hose or cracked housing, failed gasket or water pump, sometimes the engines cooling system needs to be inspected from below or inspected using a mirror and flash light.
I agree. You need to get the system pressure tested to confirm the leak. Coolant can leak from 20+ different places on any vehicle. If you would like us to look at it just call me and schedule an appointment (313-562-7022). I am sure we can figure it out for you.