Update.
Duct arrived and pressurization is now good. She makes the full 4.2psi, albeit at Max Flow, still. I can live with that, but they're still sealing some stuff up, so they're hopeful she'll be able to make it at Normal flow.
But.
Upon run-ups, they noticed fuel leaks from FCU where it attaches to engine on LH side. Hoping it was just a leaking gasket, upon dismantle it turned out to not be. It's actually a leak inside the FCU. Sigh. They found a tagged one for $7800, or I could have it sent in for repair. The average repair is apparently around $5K, but they say that if the drive shaft is worn, it can easily be $10K. I went for the overhaul and took my chances - will see where it ends up.