Well from my understanding. The property cannot be exempt from cgt at all, as it ceased being your main residence for 6 + years, while you have used it to produce income. section 118-45(2) core tax legislation.

however, for example if you did use it as main residence every 6 year period, you would be able to claim. you would work it out by capital loss/gain X non-main residence years/days in your ownership period. section 118-185(1) (2) core tax legislation.

However, I would seek advice from a qualified professional, as I'm not a qualified in this area as of yet . Hope this helps at all.