Anything is possible, but the only way to tell if there is a hairline invisible to the eye crack would be a pressure test. If you know any auto mechanics or have a local shop you could bring it to, they can leak test the entire system. But if coolant is leaking down the frame, can you notice if it is coming out of the overflow hose? If so, that would indicate a definite pressure leak in the engine probably around the head, and if the O rings are new, it would mean the head is warped.