Even if the problem is with the external wall, which is probably common property, the owners corp may invoke section 49 of the Act which says:
OWNERS CORPORATIONS ACT 2006 – SECT 49
Cost of repairs, maintenance or other works
(1) An owners corporation may recover as a debt the cost of repairs, maintenance or other works carried out wholly or substantially for the benefit of one or some, but not all, of the lots affected by the owners corporation from the lot owners.
(2) The amount payable by the lot owners is to be calculated on the basis that the lot owner of the lot that benefits more pays more.
(3) The works referred to in this section may be to the common property or a lot.
Your best bet here may be to argue that while the repairs directly benefit your lot, they would also benefit the building as a whole and therefore the costs should be shared.
Having said that, there are many elements of Victorian strata law that are a total mystery to me. Put a call into Consumer Affairs Victoria or talk to a strata lawyer to get a definitive answer.