I really feel for you in this unfortunate situation. The owner is very irresponsible. But I wonder who is paying the rent?
I’ve found that if the EC makes the issue known to all other owners in the OC, it can get results. But you need to be sure that the offending owner is aware that everyone in the OC is being informed of the situation and that if the matter goes to the CTTT all of their decisions are made public on the Australian Legal Information Institute’s database ( https://www.austlii.edu.au/form/search1.html?mask=au/cases/nsw/NSWCTTT ).
There are no privacy laws here – this is an OC matter and it is perfectly OK to inform the whole OC of the situation, of any EC correspondence on the matter and of any actions taken by the EC.
My experience is that owners, when genuinely in the wrong, wake up and finally do something when they realise that all other members of the OC know about the situation. They also don’t want to risk having a very accessible public record of the situation on the Australian Legal Information Institute’s data base.
And if the owner still doesn’t do anything then start the process that sees the matter go to the CTTT.
I’m sure others here will offer advice too.