Yep, done that. I think the water leak is close to the drain pipe that flows to the street. I was going to try checking in a line from the drain at the street straight to the house where the gutter downspout is. Might be along that line. A couple of the heads are right on that line also.
Sometimes, you need to cap off the heads in the leaky zone, to get enough water flowing to show itself at the point of the leak.