intake manifold gasket (GM3800) gone bad then good?

L26 engine, low mileage, but 15 years old: When starting in the morning, misfires and spews out white smoke. Pulling off spark plug leads, it appears that the cylinders 5 and 6 are the guilty ones. But once the temperature guage reaches 1/4, the smoke stops and it runs smoothly. So the white smoke usually means coolant from a buggered gasket. Intake manifold gaskets are a common failure on old GM3800 engines. But why only part-time problem? Is it possible that when the engine is hot, the gap in the gasket is closed?