Brass Champion/Superior Sprinkler Controller/Actuator Slow Drip

I've replaced all the rubber parts on my sprinkler controller (see the diagram of similar unit), but it still continues to have a very slow drip (inside the line). There's no visible water on the outside of the controller, but if I remove the anti-siphon cap I can see a slow drip. The unit

Superior - Superior Model 800 Electric Valve Adaptor Brass — Sprinkler Supply Store

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TFP Fire Products Catalog Americas 04 21, PDF, Fire Sprinkler System

SUPERIOR ACTUATORS 3200 - Ewing Irrigation

Champion, CL-100-C

Understanding 24VAC Sprinkler Valves «

Understanding 24VAC Sprinkler Valves «

Valves & Actuators - Irrigation Express

Valves and Actuators

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Champion Irrigation AA – Arrowhead Brass and Plumbing, LLC