Q: I got p0133 after fixing exhaust manifold leak

My car 06 suzuki forenza 2.0. Had small exhaust manifold leak aver since i bought it. The leak got bigger few months ago and started ticking, so i sealed up/fixed it. (the upstream sensor is attached to the exhaust manifold) But ever since i sealed the leak, im getting p0133 And it comes back after resetting the car few times. It seems like the Ecu got used to the leak for so many years so that when i sealed it, its throwing off that code. I looked at the sensor, it looks ok, the wires seem fine. Should i change the sensor? And by the way, sometimes the CEL goes off by itself and comes back on a day later.