Hello Anthony
If your scheme has not made any changes to bylaws over the years and is still operating on the basic laws, then windows are considered common property and the OC is responsible: write to your Strata Manager and explain the problem and ask for it to be fixed.
However, if the windows were replaced over the years, there may well be a special bylaw which makes it the lot owners repsonsibility: you would have been given a copy of your scheme’s bylaws when you bought the flat, so the answers will all be there.