Bill,
After checking the caulking around the corners, wall to pan, shower door, and valve plate, you may want to check the drain itself to see it that is where the leak is. Sometimes the drain needs replacement.

Some of the old leaded-in styles need the lead tightened up (can be done by punching a line in a circle around the lead to expand outwards)

Sometimes the caulking has dried, or fitting cracked.

Sometimes a rubber seal is crooked.

Terry

• Shower drains, (click here)