I have a leak in my shower. The hot water drips when the hot water is off. I pull the casing off and there were no leaks. I think the washer is damage in the connecting pipe

Tell us more. Brand of shower valve? Leaking from, the spout? The stem? The shower head? One handle or two knobs? How old? Back to you, Tom

Leaks where, from the shower head, from the tub spout, around the handle? What do you mean by casing?