The information on this literally doesn't exist yet. They're discovering it right now by trying to actually re-fly the first rocket. As they re-fly more of them

The information on this literally doesn't exist yet. They're discovering it right now by trying to actually re-fly the first rocket. As they re-fly more of them, they will learn more about what wears out and how fast. Then they can build versions that don't wear out so fast and need less refurbishment using that knowledge.