Hi, I had a leak in my shower too. I don't know if you have the same issue, but this is what I found. Because new tubs are fiberglass, they move too much. This caused the caulking at the top of the tub section to separate. Not enough to see, but just a hairline separation. Whenever I took a shower the water would get pulled into the caulk line and follow it to the edge of the tub and down the side. It was invisible. It then went behind the baseboard and leaked to the floor below. Took me a while to figure that one out.

Good luck.