Talking with a CASA guy a few years back they were hoping to include Compasses in CAO 100.5 . Until then it was in an AWB.
An Airworthiness Bulletin (AWB) is issued to inform the aviation public, in a systematic way, of essential information not considered mandatory.
CAO 100.6 was repealed in 2007.
So why mandatory every two years? . Surely if servicable you would just use until proven defective. Unless dictated by manufacturer or SOM
Happy to be proven wrong