If this part leaves a black residue on your hands, it's hinting at replacement. First, the technician will cut all the moldy caulk from the shower pan or the tub tub. Go ahead and remove both stems and continue up which one is which, it matters on many valves. https://bleezlabs.com/demo/quora/adonis/index.php?qa=599381&qa_1=home-faucet-repair-construction-plumbing