When you loaned someone your car, and the car came back in a bad condition, most things are not working like hooter, reverse lights, windows cracked, etc., can you legally demand him/her to fix the car? I am in South Africa.
I can't speak directly to South African law. I am an American (but not a lawyer). Much of the relevant American law is derived from English common law, and I will assume for the purposes of this answer that this is true for South African law as well.
In this example, you lent a car to a friend, and from the sound of it, primarily for the friend's benefit. (If it had been an "exchange of favors," and s/he let you use a beach house in return, a different "standard of care" would apply.) Because of this fact, your friend owes you a high standard of care for your car. Even "ordinary" wear and tear would be too much. Basically, your friend was responsible for the car's "upkeep," and was supposed to return it to you in as nearly the "original" condition as possible. Not having done so, s/he could be liable to you for getting you a "new" car of the same make, or at least a car that was no older, and had no more miles that yours had, when you lent it.