Infusion with a big enough pump does not need a perfect vacuum, although it helps.  As long as leaks are in the bag, not the mould, they will show up with air bubbles, and can be sealed.  Any air that gets in this way usually stays in the diffuser medium, so is not a problem.   If the vacuum is really poor, closer together resin inlets help, but you won't be able to install these afetr the vac is applied. 

I have heard good things about the Airvac leak detector and Etamax has a gauge that moves when you run your finger over a pin hole 12m away.  Expensive, but worth it for a boat worth  of infusions.