Warning: Turn off machine and purge the steam before completing this action.
Once Steam is purged and vacuum breaker has fallen, remove from the machine
With two wrenches, remove the body from the seat
Remove the internal teflon seat and inspect for damage or buildup
Remove the internal pin and inspect the gasket, it could be brittle which would need to be replaced. In a pinch, a steam tip o-ring can substitute, but is not a permanent solution.
Clean he internal seats, refit, and reinstall.
Wrap three wraps of teflon tape around threads of vacuum breaker
Reinstall into the machine, only tighten until the vacuum breaker seats against the crush washer.