Normal for a leak to go away? No. But the water outlet (a plastic part) does have a history of cracking. It may fail catastrophically. Note that having your engine overheat can warp the heads and lead to a major repair bill. Treat the overheat light like you would a oil pressure light - take action immediately and avoid having to limp anywhere. Warranties do not cover engine damage due to running in a overheat condition. GM doesn't care how much the kids begs.