if it turns out that a previous owner did unauthorised work that contributed to the current problem, then you, as the ongoing owner, could be liable for some of the cost of its remediation, as well as contributing to the levy costs.
Generally speaking, if changes to common property have been made without a by-law assignng responsibility for the upkeep to the owners making the changes, the responsibilty reverts to the OC. This is a default position that is intended to make sure that OCs require owners to get by-laws for changes. Sadly, too many changes are made on a nod and a wink. Subsequent owners can be faced with the dilemma of accepting a new by-law or having to allow the OC to return the property to its original state, albeit at the OC’s expense.