We've noticed that the central bathroom shower/tub hot water is difficult to turn off completely. So we suspect that the washer in the shower "Hot" stem needs to be replaced.
We first turn the water to the entire house off (out by the water meter) so that we can work without leaks.
We first remove the cold water handle, escutcheon, and stem.
That gets us access to the washer, at the bottom of the stem. The washer is held on with a screw.
We have a partial package of 3/8L Beveled Washers, and that seems to fit the stem, so we use them.
We reverse the process for the cold water to reassemble it. Then we repeat for the hot water. Then we can turn the water back on out by the driveway, and we have new washers for both stems.