The musty smell is telling you something
Sydney humidity plus a dark, damp coil is perfect mould habitat. Once it establishes, the unit seeds the room with spores every time it runs — the smell is just the part you notice. Wiping the louvres doesn't touch it; the growth lives on the barrel fan and deep in the coil fins.
What we do about it
Full strip-down clean of the coil, fan and drain, all washout captured in a sealed bag, then an antibacterial sanitising treatment of the airway surfaces. You get before/after photos of your own unit, and the smell leaves with the mould.