Looking at that picture that appears to be the left side valve cover? If so you have a coolant drain just above where the oil filter mounts. Could be loose or the sealing washer leaking. If you look up as if laying on the ground under the bike between the valve cover and oil filter is a small bolt head that is 10 mm. It is used to drain about half the system for service. A pressure tester would help as mentioned.
Behind "Goldwing" Bars
I'm Claustrophobic so I ride a motorcycle