I purchased a Rainbird SAM 1800 pop up with the intent to stop an irrigation pop up station from seeping . It is the lowest irrigation pop up on the zone.
There's obviously something wrong with that SAM. Perhaps the rubber washer is missing where it seals. Could be debris in the sprinkler. Could be a 1804? with a SAM cap on it. Could be the only working head on the line?
--
None the less there's still a problem. If that seeping is 24 hours a day you have a problem with the valve on that zone.
Most likely the diaphragm or seat washer needs replacing. It might have debris stuck in it. It might be loose.
It could be a hairline crack in the valve seat.
The solenoid might be a tad loose.
If I knew which valve you have I might be able to give specifics.