If a rider's motorcycle helmet has sustained a significant impact during a road accident or a high-velocity drop, what action should be taken?

1. The helmet must be immediately retired and replaced, even if the outer shell appears unblemished and scratch-free
2. The helmet may continue to be used indefinitely as long as there are no visible external cracks in the polycarbonate shell
3. The helmet can be restored to full safety by applying automotive touch-up paint over scuffs
4. The outer shell can be soaked in warm water and detergent to expand the crushed interior foam liner back to its original thickness