The shower control in our bathroom is a Delta (presumably dating from about 30 yrs ago when the house was built) with the ball-shaped handle that turns to adjust the temperature and tilts to adjust the volume.
We thought of replacing it with a more recent Delta with a different style handle and with the built-in thermostat. I assumed that I could simply unscrew the old innards and replace them by the new innards, but the guy in the plumbing dept. at the hardware store said, "No way." He even said that we probably would not be able to replace the old innards by new innards of the same style because the design has changed over the years: the only thing to do would be to get into the wall and disconnect the whole unit and replace it with a new one.
Is he right?
MB