The truck blocking your way to the airfield won't let you by. But if you were to put a little oil on the road, it might spin out of control. Go to the Golf filling station in Bastion Falls and in the space behind it you will find the can. Throw it on the ground infront of that truck and it will slip into a ditch.
You were familiar with oil; you worked as a machanic all day! This was your tool. You loved being a machanic and so did Amelia. She always liked that about you. This was your first step toward being able to fly.