Using one pint of coolant in over a year isn't a big deal. That's why there's a place to check the level in the first place. Of course the best thing to do would be to pressure test your cooling system, including the cap. Water pumps often leak when they're not running or not under pressure, like sitting over night. But you say you have no spots or puddles. Visit your local chain auto-parts emporium and borrow a pressure tester. Get the system up to operating pressure and see how long it holds. Then test the cap. Watch out for exploding plastic radiators, too.