I need help on the best way to proceed with a leak problem. We have a all-one piece shower/tub combo that has a leak going on in the wall when the tub spout is pulled to divert the water up to the shower. We have replaced and tightened the spout and shower arm but it is still leaking through and coming into the kitchen ceiling. It does not leak when only the tub is used, just when showering. I am sure the unit was put in before framing was completed becuase there is no way to get the tub out without cutting it apart. Any suggestions on what the problem might be? Is the stop-check valve likely to leak only when showering?? Because of the small fiberglass opening it is very hard to see back there. Thanks