GL1800s are notorious for hose clamps leaks. They have over 44 of them. Assuming that the drops were found towards the front of the head, you may find that the cowl will need removed to get to the 2 clamps at the front of the radiator. It's best to test the system using a pressure tester. Many can get those on loan at a local auto parts store. Be sure to test the radiator cap too.
Pull the lower, the upper, and the inner cowl on that side. Never does Honda point the hose clamps inward making access to the clamp bolt easy. On many the clamp bolt point outward. That usually requires the cowl to be removed. If the cowl needs removed, I usually replace both sides with aftermarket hose clamps on each side (2-#4s and 2-#10s). The reason is that the aftermarket ones have more surface area. They're pretty much the only ones I always replace when they leak. Because of on-coming wind blasts, and even though those front hoses are protected by the cowl, there is a lot of flexing in the cowl and that flexing can pull on those hoses. When I replace them, point the clamp bolt inward and between the hose and the rad. On some, I find the bolt pointing forward ... sometime those can be tightened without removing the front cowl.
To tell which one is leaking, you'll should see anti-freeze puddling at the top of the hose. Use a mirror and a flash light.