A tough one, here.
If you have sorted out the other subjects (evidently without any trouble), then it wouldn't appear to be a case of exam jitters for the one subject in question.
That leaves, as a likely (?) consideration, that you have been concentrating too much on practice questions/papers to the detriment of basic technical understanding and, perhaps, deluding yourself along the way that the understanding was OK/adequate. That's fine if the next question is much the same as the last but, as the examiner so often does, that next question is tweaked a bit so that basic, technically competent, thought processes are necessary to sort out the answer, Then, any deficiency in technical understanding can be the straw which breaks the camel's back. The worst aspect of this scenario is that the candidate is left totally bewildered after a good run of practice test work. The other aspect is that it can be very difficult to self-critique, identify, and come up with a suitable strategy to address the problem(s).
At this stage, I wouldn't rush off to find a tutor - not the least problem of which relates to finding one who is sufficiently technically competent to warrant spending your hard-earned money - especially as your other subject successes suggest that you should be able to do what is a reasonably straightforward subject principally from self study. What may be the problem is that you are heading off at a study tangent while not being able to detect your basic knowledge deficiencies. First, you need to identify where your problems lie and that should be fairly easy for a competent instructor to do via some assessment work.
As an initial gameplan, you might consider getting a competent instructor (not a CPL mate who just managed to scrape through the exams himself) to spend an hour or two with you to suss out whether your knowledge and understanding of the basics is up to speed and, if not, why not. It then should be feasible to determine an appropriate strategy to overcome whatever problems may be the cause of your bedevilment. I don't think for a minute that your problems will not be amenable to solution.
Keep in mind that multiple fails create problems for CASA (
www.casa.gov.au/standard-page/re-trainin...ods-and-exam-windows) and you are going to need to spend some time/dollars with an appropriate instructor to tick the CASA box prior to their giving you the nod to re-attempt the exam. Just view the exercise as a minor hurdle to clear in the track race to get to the licence at the end. Have a look around you and I'm sure you will see others who have less aptitude who have passed the exam OK - your pass won't be an undue problem, just a minor hurdle to clear.
With the PC technology available today, you should be able to take your pick of available instructors (despite geographic/covid problems) and run the exercise via direct one on one PC hook ups using software such as MS Teams or your selection from a bunch of the other stuff in the marketplace ...
Main thing, for the future, is not to allow any similar problems to progress to the CASA stumbling block situation - if you miss out, say, twice, it is essential to fix the problems before the third exam attempt.
