Adding my solution for anyone searching for this. I purchased an Orbit 3/4 and 1” Brass Anti siphon valve repair kit item 53066 from Home Depot for $10.
The seal on the valve that moves up and down was cracked causing the leak. The kit had a bunch of stuff, but I used the seal for the cap, the valve seal, and a replacement plastic valve and it was good as new.
The hardest thing was finding a wrench big enough to pull the cap off. I had to resort to using big vice grips almost all the way open to break the tension on the cap.