On Fri, 23 Mar 2007 04:08:08 GMT, Grandpa wrote:

Take off the valve handle, and unscrew
the valve stem nut, then the valve stem. Oh didn't I tell you turn
off the water first? My bad, but its a tub isn't it? Anyway, stick
your little finger (unless you're ham handed) into the valve and
feel the seat for roughness. If it feels rough, then you will need a
seat resurfacing tool.

Some seats are replaceable. Look inside the hole and see if there is
a slot in the ccurrent seat (interrupted by the hole through which the
water goes.) A flat screwdriver removes the seat. But like he says,
only if it feels rough.

IIUC the roughness chews up the washer, and I guess makes it harder
for even a new washer to seat. Also iiuc, the seat only gets bad if
one continues to use the faucet after the washer is so far gone that
the metal end of the stem rubs/scrapes on the seat when one struggles
to close it tight enough to stop the dripping. I don't mean that all
such struggling causes metal to metal rubbing. I would think that is
pretty rare and takes a while to do damage.

Now take the stem(s) to your local hardware
store of choice and look for the replacements.
All covered he
http://www.ehow.com/how_117402_fix-faucet.html