If you are constantly being pulled over by this one boofhead, you may have a fair case to complain to his commander.
If SA is anything like NSW, there could be a record maintained of each RBT check, at least for name, time and date of check. If you are only being pulled over at random, and not in a declared RBT stop zone, a notation should appear in the officer's notebook. Are you aware of him making any notations in his book whilst speaking to you? In theory, every stop you have alleged should be recorded and the Commander can check to see if you have been pulled over as often as you say. If no record exists, do you have witnesses to support your claims that he stops you as often as he does? If you have witnesses and can prove that you are being stopped as a daily occurrence, it will be up to the officer to explain why he feels this is necessary. Whilst he has a responsibility and the authority to stop you for vehicle, license and sobriety checks, it doesn't mean he can do it every day.
You have two issues. The first is the daily stops - that is over the top, even in a small town. The second is the fact that after about fifteen stops, he finally decides to tell you your car is defective. Why not the previous 14 or so stops? This certainly gives the impression of harassment, unless you modified it between the 14th and 15th stop?
The problem is, some cops love the power they feel they have over younger drivers, especially in a small community. You never know, others might have already complained about this bloke too and his commander might not be too happy to receive another complaint.
The thing to remember is this. If you are driving within the law when he stops you, he has no right to continue doing it as frequently as he does - that is definitely harassment. He could be playing on the fact that you are not likely to complain for fear of retribution, but he has far more to lose than you do if he is spoken to by his Commander and continues pestering you.
Find out where the area commander is (not the local Sergeant - you need a Commissioned Officer) and make an appointment to see him. Take witnesses if you can. Good luck.