Pro Systems 850 trouble.
If it does not leak by with engine off and pump on, then pump,pressure, and needle and seats appear to be fine.
If it leaks out boosters only when idling, it is possible idle curcuit is not functioning and it is trying to pull fuel over the main curcuit to keep running.
Maybe the front throttle plate is open too far and the idle transfer slots are uncovered and need to be closed more to let idle curcuit work. You could try opening the back barrels some to compensate for closing the front ones.