It sounds like you would have benefited from good advice and help from a knowledgeable strata manager to avoid what sounds like a stressful situation.
If this happened in Victoria, Lot owners should remember to take steps to actively maintain any part of the property which is owned by them. In Victoria, the courts presently view the legal ownership of a private balcony waterproofing as part of the private lot property.
Section 129 a) of the Owners Corporations Act 2006 applies – Care of lots
A lot owner must—
(a) properly maintain in a state of good and serviceable repair any part of the lot that affects the outward appearance of the lot or the use or enjoyment of other lots or the common property
Lot owners need to consider that the Water act of 1969 establishes the liability of the lot owner for damage caused by an unreasonable flow of water from their land to another’s land.
Builders are also liable for faulty materials and workmanship. This is generally a period of 10 years from the date of completion. This is established in the BUILDING ACT 1993 – SECT 137C Warranties for purposes of homes under section 137B
It sounds like your contents insurer provided cover for the legal liability for the damage to other lots.