say you fix it and it cost you R15k for that matter. Afterwards you have a car which you know has brand new parts in and will last you years to come (unless some other major thing goes).
So situation a) Fix it for R15k and have a reliable car again
b) Buy a car cash from your savings and also sell the old one. Now you sit with someone else's problem and you paid them to have it (unless of course you drop R150k on a relatively new small car, which is not guaranteed problem free just yet)
c) Trade the old car in and buy a newish decent car. So firstly you get screwed out of money by the dealership as obviously they need to make money on both ends of the deal. Don't think your monthly payment would be less than R1500, so 10 months later, you would have paid all your repairs and you would have known the condition of everything in the car, something you cannot know on a secondhand car you bought now (Yes Dekra and xx point safety checks are a thing, but they don't strip it down to the bolts to inspect it so small things will pass them by)
Honestelaly (yes that is a word in my Engrish dictionary) I would go with option A but I too am in the process of wanting to sell my small car to buy a small bakkie. But its not an itch, it's just that the wife has a car should we need more than two seats, and the loadbin would come in mightly handy for doing some sideline work. Not planning on upgrading, looking in the same pricerange