Car engine problems

I bought a car at a dealership and i was also charged for it's repairs and was added to my finance. Before I left I saw an engine light on but was showing service but the service had just been done so they said it will go off but if it doesn't I can notify them. Few days down the line the car gave problems which includes oil leak, no power, hard gears and I told them. I was told to bring the car back so they can fix it. At this point I felt if the oil is leaking and gears and no power there is more problems coming up and I told them I no longer want the car as I foresee it costing me. I was told they cannot return it as it is withing their CPA rights to fix the car. They stayed with the car for over a week and was told that the tappet cover gasket and oil cooler that need replacing. I told them these were not mentioned when purchasing the car and I cannot take a car that is starting to give engine problems.They responded as ff: "These were obviously latent defects that did not require repair at the time of purchase. Again, we will not be able to reverse that sale as we reserve the right to repair first as per the CPA" The aftersales people are so arrogant and cannot even assist you. I offered an option of changing the car and still refused. Worst service