The water hammer angle might be worth checking too, not just the torque on the packing. If the valve closes quick on that manifold, the shock can shift the stem just enough to wreck the seal over time. A slow close or a check valve upstream might save you more headaches than retightening those glands.

Louie was probably half right, but f/8 is more of a starting point than a law. The real trick is knowing your lens and your distance. At f/1.8 you gotta be sniper-precise with that focus ring, and even then, breathing after you lock it can throw it off. I shot a whole roll like that once at a family picnic, got maybe 3 keepers out of 36. These days I'll shoot wide open if the light is trash, but I focus on the eyes and then stop down to f/2.8 or f/4 if I want any margin for error.

That process of elimination is exactly what separates real field experience from lazy pattern matching, so the time spent was the point, not the problem.