The exhaust flue is presumably common property because it’s outside the cubic space of the unit. The OC thinks the purchaser should pay for rectification because the fault was caused by the former owner. Is there a ruling on this?
There’s nothing in strata law specifically about this but IF the flue is common property and the vendor is long gone, then, in the absence of by-laws that say otherwise, its Owners Corp responsibility.
That’s why the common property by-law insists that the lot owner or the owners Corp has to take responsibility for changes. And that’s why “nod and wink” approvals for changes to common property are such a bad idea.
At some point your OC or committee members have decided to ignore work they must have known was going on. Now all the owners in the block are paying the price.