Regardless of what anyone else says on this thread, I think it’s best that you seek specialised strata legal advice.
I agree.
I’ve dealt with dozens of these water ingress issues in VIC. And, I regret to say, owners have usually get the actual eventual issue totally wrong.
So it not only needs professional investigation but it also may need profession opinion about maintenance responsibilities.
Unfortunately, I regret to say, IME professional investigation has often got the issue totally wrong as well. They can very very tricky issues to solve. The professionals can need to be top notch experts and not just a regular plumber/builder.
Still, in VIC cracks in walls marked “Exterior Face” and general waterproofing around the airspaces of their lots (inside or outside) is a legislated lot owner responsibility in most cases. In VIC, an outside balcony, terrace or courtyard is usually treated like an inside bathroom as far as surface treatments including tiles and waterproofing is concerned.
If enough lots are being affected, the OC can decide to do investigations/repairs. Deciding to repair lot property needs a Special Resolution in VIC which is not always easy to obtain. But if most lots need the works it would be more likely.