I have had my 33 gtst for 2 years, and traveled to QLD and back from Canberra once, many Sydney trips, plus coastal trips as well, also WISD and not once has it ever used any oil. So i think there maybe a problem buddy get it checked out you may have excessive blow by, check the intake pipes for that. Good luck
also do a compression test that may shed some light on the problem, change oil. I use a 10w 50w semi senthtic