To repair a leaky Delta bathtub faucet, replace the worn rubber seats and springs. If the faucet has a handle for each temperature setting, feel the temperature of the water leaking from the spout to determine which handle needs to be repaired.
Close the main water valve for the house to turn off the water flow. Find a separate faucet and turn it on at a slower flow to expend any excess water pressure. Use an Allen wrench or a Phillips screwdriver to loosen and remove the screw from under the faucet handle's cap. Remove the handle either by pulling it off or using a pulling tool if it is stuck in place. Under the handle, remove the nut from the stem of the faucet using an adjustable wrench.
Remove the stem from the faucet and strip it of the rubber seats and springs using tweezers. Use plumber's grease to cover the new seats and springs before placing them into the faucet. Use plumber's grease and cover the ball at the end of the valve stem.
Replace the stem and secure it with the nut. Replace the handle and secure it with the same screw or a new screw with the same dimensions if the old screw is stripped or rusted. Replace the faucet handle's cap and turn the water valve back on to test the faucet.