When an aircraft arrives with an inbound write-up and months of history on cabin in-flow pressurization problems, you should pretty much assume ONE thing. It's got-a hole in it.
We took this thing to 4psi differential and "walked" the aircraft with three people. Some cargo door seals were puking a "little", but when a hand was drawn across the A/C hook up doors....... the problem was pretty much obvious before the aircraft was equalized and the access door opened. (and NO.... the mechanic did NOT want to even open a simple non-sealed door, because there really was a huge amount of air coming out the edges)
I'm glad the problem was found. I'm not glad it took 2+ months of flying around the system with 10+ write-ups....... pretty piss-poor.
MD10-10 ATA 21-31-00 Pressurization
Fault Isolation Manual 21-31-00 Task 803