When Hawkeye is being instructed to go see Kyung Soon's Mother. Potter, Hawkeye and Kyung Soon are standing in front and the left of the car. When they cut to the scene where Potter is handing Hawkeye the medical bag. They are now standing almost at the rear of the car just next to the back passenger door. Then is switches to a front few of them and Hawkeye walks back to the front passenger door to get in and Kyung Soon turns and walks directly across the front of the car.
Kyung Soon would not be able to obtain petrol for her car as her home is near the M*A*S*H hospital which itself is near where the fighting is. Surely any petrol would be requisitioned by the South Korean military.