Automatic sprinkler valve leaking

This is an old Champion 466 valve fitted with a solenoid conversion kit. When it comes on the water gushes out the anti-siphon part of the valve rather than going to the sprinkler.
The question is whether it's the anti-siphon valve that needs a repair kit or the diaphragm and seals in the actuator. Anyone here happen to know? Just want to have the right parts before shutting off the water.
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