Builder insolvent, major waterproofing defect discovered 9 years later – do I still have any rights?

I own a townhouse that was completed around 2017. I recently discovered a leak from my ensuite shower after noticing a small damp patch on the ceiling below.

After investigating through a downlight opening, I found mould and water damage on the underside of the floor sheeting beneath the shower. I have since obtained advice indicating the shower waterproofing system and/or shower base has failed.

What makes me think this may be more than normal wear and tear is that an owner of an identical neighbouring townhouse in the same development previously experienced a similar issue. During their repairs, they advised that no waterproof membrane was found between the tiles and floor substrate.

The complication is that the original builder is no longer trading and appears to be insolvent.
From my research, I understand:
Domestic Building Insurance (DBI) generally covers structural defects for 6 years and non-structural defects for 2 years.
Building defect actions under the Building Act may be subject to a 10-year limitation period from the Occupancy Permit or Certificate of Final Inspection.

I am currently trying to obtain the Occupancy Permit, builder details and any DBI documentation from the Owners Corporation.

My questions are:

If the shower waterproofing was defective or a membrane was never installed, would this generally be considered a building defect for the purposes of the 10-year limitation period?

If the builder is insolvent and the DBI period has expired, are there any other avenues of recovery available?

Is there any practical benefit in pursuing DBDRV, VBA or legal advice before undertaking repairs?

just trying to understand whether there is any realistic pathway worth investigating before spending approximately $10k+ on repairs.
Thanks.