Hello
I live in a relatively new 2 storey duplex and my downstairs ceiling is leaking. It’s happened in the past before and the builder came back to inspect and couldn’t find anything including doing some waterproofing via adding silicone everywhere, around any gaps they could find from the roof. Since then it appears to have held up ok over the last year or so including a few large weather events. However atm in Sydney we are getting some serious wind and rain and the leak happened again last night.
Previously the builder blamed that an adjacent down pipe may have been blocked and caused the water to backup and not drain properly… but this was never proven and there was no blockage even after I had an independent plumber come to do a camera inspection. We’ve even done a flood test of the balcony multiple times and detected no leak.
It’s hard to describe but directly above the ceiling where it’s getting saturated is a balcony as well as a drain. I suspect that water could be entering some crevices against the exposed wall/windows and somehow with strong winds there is enough getting in and seeping through. I'm concerned about any potential future moulding/structural impact. The leak doesn't appear to occur during regular normal rain, just when it's really windy. I could ask the builder to come inspect again, but last time they just blamed a loose roof flashing or gutter overflow and explained that water will just get in... That doesn't sit well with me.

What’s the best way I can try and find out the root cause and have the issue repaired once and for all?
Should I be drilling a small hole in the saturated ceiling panel to relieve any potential water build up? Is it likely that my ceiling panel downstairs and inside will mould? It’s discoloured a bit from the previous leak and doesn’t appear to be any mould from the last even a bit over a year ago
.
I lose sleep whenever there are significant rain events! 🙁
Thank you