I have a steam shower that's over 40 years old. Everything works great but the shower drain pan is cracked from the wall to the drain. How do I replace the drain pan without damaging the marble Marlite walls?

What is the pan made from? Are there any signs of water damage below the shower?

I'm assuming that you have a plastic or fiberglass shower floor.
Am I correct? If you don't wish to replace the floor, they make plastic and fiberglass repair kits if you tell me what you have I was see if I can help. Back to you, Tom