Leaking anti-siphon valve?

Hi-
One of the anti-siphon valves for my system seems to be leaking. If I shut off the water to the irrigation system altogether then the leak stops, but as soon as I turn it back on I get a slow trickle coming out of the anti-siphon part of the valve continuously. This is a basic Orbit 3/4 anti-siphon valve from Lowes.
I opened the valve up (both the anti-siphon side and the valve side), and inspected all of the parts and everything seems to be in good shape, but obviously there is something not right here. Any suggestions? Is it more likely that the problem is in the anti-siphon side, or a slow leak coming from the solenoid side?

Thanks in advance!

You didn't say if this is a new or old valve that is leaking. You also didn't say where at the Anti-Siphon that it's leaking at. Housing, seam, threads? I wouldn't normally waste a lot of time hunting down and diagnosung problems. With my hourly rate, it's less expensive to just replace the valve.

Did you examine the lower part of the housing when you had it apart? Was it cracked?

Mick