Bah, I’ve worked for hours on this, and nothing fits. It’s fine though, I’ve realized that ‘Finn’s familiar with the weapon system, he worked on the base’ is audibly identical to ‘Finn’s familiar with a weapon system, he worked on the base’.
So I’m fine with leaving it as it is, and leave it up to interpretation as to whether or not Leia was aware of its existence before this moment.