You can test a ST's cooling system for leaks the same way as you would test an automobile. Go to the auto parts store and borrow a Cooling system pressure tester. Alternately you can get them off ebay. The tester is basically a little hand operated pump with a gauge on it that has on the end of its hose, an adapter for the radiator. You hook up the adapter to the radiator, pressurize the system with the amount of pressure of the radiator cap (14-18psi) and let it sit. If the pressure drops in 10 minutes or less, you have a leak and usually you can hear it hissing from the defective part. If your cooling system checks out OK you can put a different adapter on the tester and test your Radiator cap. You pump up the tester until you hear the cap "pop off" and you confirm that it is doing it at the correct pressure by watching the gauge. The hardest part about using the tool is knowing which adapter you need for each particular radiator or cap. The Stant brand tester, which is the most common one out there, uses a #12027 adapter for the Radiator and #12021 adapter for the cap. I am relatively sure these are the same ones for the 1300 and also some goldwings. Hope this helps.