My walk in shower door has a plastic strip at the bottom to keep water from leaking out onto the floor. The plastic stripping has broken off in places and water now leaks out while showering. Can I replace this plastic stripping?

Sometimes a little hard to find but yes. The strip either screws on or slips into a groove. I have used door sweep replacements for this problem. They are found at HD or Lowe's and are very inexpensive. In the meantime, move the showerhead so the water sprays away from the door.