Is a side gate common property?

We are a strata plan of four town houses. When they were first built in 2005, the lots were divided with colourbond fencing and matching colourbond side gates. Now the gates need repairs but the strata managing agent claims the gates are not common property and that each owner is responsible for the cost. Side gates do not appear on any list of what constitutes common property and on the site plan are outside the thick lines delineating the buildings.

Is there some precedent that includes side gates as common property?

Is it possible for the Owners’ Corporation (there are only four of us) to introduce a by-law naming the side gates as common property?