Should I keep the car I have or trade it in for another used one?

I have an older (1994) Toyota Camry. I bought it 4 years ago fairly cheaply, and I’ve had to make some fairly expensive repairs. In fact, it just came back from the shop today.

After this latest repair, it runs the quietest it has ever run since I bought it. I’m really pleased about that.

I’m not pleased that my regular mechanic, whom I trust, found an oil leak in the valve cover. He cleaned it thoroughly and instructed me to watch it closely for signs of future leakage, saying to bring it back in at the first sign of any oil escaping.

Am I best to just keep this car since it now appears to be running better than ever before, or am I best to trade it for another used car while it’s running at its peak hoping to get the best trade-in value?

My financial situation dictates that I will have to buy a used car. I simply cannot afford a new one.