The bad news is that, according to Section 77 of the Strata Schemes Management Act, “Distribution of surplus money in administrative fund or capital works fund,” your owners corp can only repay surplus funds if there is a unanimous resolution to do so.
The good (but not great) news is that under NSW strata law, a unanimous resolution is one that is passed with no votes against. In other words, you just need everyone at a general meeting to agree or abstain. You don’t need every owner in the block or at the meeting to agree. On the other hand, one vote against at the meeting would kybosh the refund.