I just moved into a new home and the anti siphon sillcock on the outside of the house is leaking from behind the knob. I tried to remove the handle via the center screw but it was rusted so badly it broke. The handle still wont come off. Any thoughts on how I can do this? I assume I just need to replace the seal behind the handle...
Is it leaking at the stem or is it actually leaking at the vacuum breaker? The breaker can allow a leak (or a gush) and the parts are replaceable (if you can find them - which you likely won't due to age). A plumber would suggest replacement as that is the quicker fix and cheaper since time is money.
I'd replace that one with new and try to fix the old to be a replacement if needed later. You'll be a step ahead next time.