I had a similar issue in my place in VIC. It was very similar to Moo102’s experience from my committee too – a reluctance to take responsibility unless evidence showed it was an OC issue.
Over the course of five years, a mysterious ingress would take place in colder months only and always around the entry walls inside my apartment. Investigations by the OC plumber were inconclusive during the intervening years and I was forced to go 50/50 in costs a few times with the OC even though the problem was unsolved. Fast-forward to the fifth year and I proverbially lost it with the Strata Manager and said we needed to solve the problem, no more 50/50. By that stage the common area walls in the outside stairwell above our property were wet to the touch. Finally we had good service from the OC plumber (a different plumber who was totally onto it and sympathetic with our issue) and he forced entry into the apartment above (they were obstructing entry to OC plumbers for years) and found their shower wall was buckling and filled with water. He shut their water down at the mains and then proceeded next day to take to their bathroom with a pick axe or the like, water rushed out like a torrent. It was their showerhead that had a break in the pipe join – that was never fixed by them. He fixed it and they were billed thousands of dollars of OC plumber time to essentially replumb their shower and rebuild their bathroom walls.
Long story short, zero compo from the horrible owner above, zero compo from the OC, but we were free from water ingress from that point on. Cut our losses and moved on, it’s easier than fighting an uncooperative owner and OC/SM for dollars if it means that the problem is solved and our sanity can be restored.
I hope this experience helps you out, Moo102 – unidentified water ingress is one of the worst things in strata!