Bantha Foodoo said:

The rebel base exposure is more of a problem since it goes against the character. Leia wanted to protect the base more than Kane wanted to talk about his childhood.

But we have no idea how long our heroes were on Yavin IV before attacking the DS. It was obviously not Lukes first time in that X-Wing. He knew the controls, targeting computer, was familiar with the weapons systems, the life support on his flight suit (presumably), knew about the flight squadrons and attack patterns ect. and knew the ship well enough to tell R2 what to fix. Also, the falcon traveled quite a ways through hyperspace. Who knows how long it took the giant, lumbering Death Star to arrive at Yavin. If a weakness wasn't found, the Rebels would possibly have had time to pack up and head out.