Thanks Whale for your comprehensive and insightful comments. Will be following up your suggestions in the coming week.
There is no record of any OC consent for any of the illegal works, but will try to obtain written confirmation of this.
Find it incongruous that individual owners cannot be held financially liable for ‘making good’ unapproved major alterations to / or removal of common property within their units but the OC can.
Ironically there is a suggestion that the sliding doors / windows may no longer be considered common property if the balcony is already fully enclosed. Isn’t strata confusing?
Thanks again for your helpful advice.