well, seeing as how a LeSabre is going to be FWD, and the exhaust manifold is typically in the front of the engine, I would guess somewhere behind the radiator on the exhaust system.
If you dont find it within the height of the engine (meaning not under the car), I would ask a mechanic. He will more than likely throw Murphy's Law right in your face by opening the hood and pointing at it in 1.2 seconds. Believe me, I have been right there and no matter how many times it happens you still feel like an idiot.
