1999 Saab 9-3 Viggen 2.3L

Good afternoon! My CHECK ENGINE light came on recently. I scanned the fault and it was P0133 (slow response from front oxygen sensor). The sensor was replaced, but the light has come on again. I am now noticing what I think may be an exhaust leak coming from the front pipe/manifold. I am guessing it could be throwing things out of balance. Is this something you could help with? Thanks!