Area-51's nailed it. Importation of mechanical items is a licence for Gubbmint, Border Force, the Dept of Agriculture, and a host of other hangers-on, to bugger you senseless, a-la Lord Flashheart in Blackadder.
Note, there is no longer any "Customs & Quarantine" Dept, either - importation controls are handled by such a multude of Gubbmint dark forces, they make a trip to Centrelink to lodge a form seem like a picnic in the park.
Then there's the Port hangers-on! My God, the charges and fees and services they can think up, would bring tears of joy to a Russian Border Guard who thrives on bribery.
There's security charges, recording fees, container storage fees, container opening fees, brokers fees, transport fees, warehousing fees - oh, and GST on top of everything ..... it's like the scenes from a crashed, and split-open money truck!
I'm still smarting in the rear end from several machinery importation exercises, and it's been a number of years since I tried it, and I have no desire to ever experience the process again.