You can do it on the bike.
It's typical to pressure test the entire system without taking anything apart other than just removing the radiator cap and installing a special cap that has a test pump attached to it. It's done by using a hand air pump to raise system pressure to the test value. The radiator cap is replaced with one that has a hand pump and a gauge attached to it. You just pump it up and see if it leaks. The typical test pressure is 15-20 psi. The radiator caps are generally rated at 8-12 lbs. (relief pressure) so you test at something above that, generally no more than 20psi.
A typical test is to install the special radiator cap before starting the engine, then run the engine up to operating temp.. Shut the engine down and then hand pump to 20 psi while the engine is hot. Do a search at "Northern Tool" for a test kit. They often come with an adapter that allows you to test the cap as well. I had a tester made by KD Tool years ago when I use to work on cars a lot. I gave it away a long time ago.
The 1800 has a history of leaking at the front hose clamps. Check them before testing. Also check for rock impacts at the front of the radiator.
http://www.harborfreight.com/radiator-pressure-tester-kit-65053.htmlOR
http://www.nationaltoolwarehouse.com/Cooling-System-Pressure-Tester-P161815.aspxOR
Call Cycle Sports on Clay Rd. and see how much they'll charge you to test the bike. I think they have a tester.
OR
A do it yourself check. You could attach a bicycle pump to the coolent hose that connects the radiator cap to the coolent recovery tank. Connect your pump to the hose at the tank end. You will only be able to pump it up to the limit of the raditor cap rating and then it will releive at that point. The manual says the cap is rated at 16-20psi. System max pressure is 20 psi. A test of 15 psi should be more than adequate because the system normally is only at 8-10 psi when the bike is at normal max operating temp of 225 degrees. Coolent temp idiot light triggers at 248 degrees and that would be about 15 psi.
The Goldwings have a history of leaking at various hose clamp connections also, of which there are many. Seems Honda is afraid of tightening hose clamps for some reason.