don’t I need OC approval to work on it?
The strata manager can usually give permission on behalf of the committee. You don’t need a by-law if you’re only effecting repairs (and the OC should be doing it anyway).
I’d hope to sort this our without involving NCAT.
Well, there’s the threat of going to NCAT and then there’s actually going. Saying you are confident you are right, so much so that you believe you will win at a tribunal, may focus the strata manager’s mind and have them seeking advice from someone who knows what they’re talking about.