Silicone works by displacing any moisture present with silicone molecules that provide a barrier between moving parts (lubricating then). The next better step is graphite. It won't run off and out of a lock assembly as easily as silicone. Best way to apply it is putting it on a key then inserting the key and working the lock a number of times followed by using a Qtip or small brush to apply some to the mechanical parts inside the door. A tiny bit will go a very long way so use sparingly. Available at auto parts stores, WalMart, Kmart.