NACE Coating Inspector
if it only leaks when the water is running, i would check the supply live going to the shower head or the tub spout. remove the plate at the valve and run the water to see if it is leaking there. that plate may have a bad seal too, so you may be able to eliminate 2 options at once. plug the tub drain and fill the tub a little. if your leak doesnt occure then it is probably the drain. if you cant eliminate the source at this point you may have to start doing some demo to get a better look.