Question
My rainbird sprinkler is leaking. I have several others that are not leaking that are  located on different zones.  The rainbird that is leaking is located in the front of my home and is on a slight decline. The rainbird is the last head on this zone and was wondering is the excess water in the pipe would still be feeding out of it due to the slope of the land.  Once the watering stops, I notice that some water comes up from the screw that adjust the rotation and then it stops. However, I place some black dirt on top and around the head and noticed that it was moist around the screw that houses the shaft/spring.  It is completely tightened and was wondering if this is a natural occurrence.
Thanks and sorry for the long question.

Answer
Sprinkler heads that are at the bottom of slopes commonly have a condition called low head drainage.  To stop this there are really two solutions.  One is to replace the sprinkler with one that has an internal check valve.  The other is to dig up the sprinkler and install a check valve just below the sprinkler.