| I just had this happen to me last night on my outdoor faucet. It's a | 'frost-free' style that has the stem washer back in the wall about 12". When | I open the valve it doesn't leak from the packing nut, but from a small | hole in the stem itself (???), which is visible when you remove the | handle...
I have one like this as well. The discharge through the inside of the stem appears to be intentional. At the inside end of the stem is a piston mechanism with a spring that pushes it into the position that opens the path to the stem and blocks the water inlet. (Closing the valve also blocks the inlet and the stem path by compressing the spring.) As long as there is enough pressure at the inlet to drive the piston against the spring and into the stem the stem path is sealed. I'm not sure why the mechanism is built this way. Perhaps they now want the reverse-check function to be referenced to atmospheric pressure plus whatever the spring adds? Or perhaps they want a discharge path for reverse flow so it won't have a chance to work its way through the check valve into the water supply? Does this have anything to do with the reduced pressure zone protector valves for sprinklers that the plumbers now say are better than the old double-check valves? (The latter do not have a discharge but the former do.)
Note that the above-described mechanism is in addition to the anti-siphon (vacuum breaker) device on the outside end of the fixture. Also, it is not an "in-use" drain for the frost-free function since it will not drain the fixture while the valve is off. The "in-use" drain is yet another spring-loaded piston on the bottom of some frost-free fixtures that opens on low pressure regardless of the state of the main valve.
Anyway, it appears that the piston can get stuck so that it does not fully seal the discharge path out through the stem. Usually fully closing the valve correctly repositions the piston, but I'm afraid the little fingers on which it slides can get bent or simply become rough with scale. Since the piston mechanism does not appear to relate to the forst-free function, perhaps the original poster has one in his normal sillcock.
Dan Lanciani ddl@danlan.*com