The 2004 Buick LeSabre came standard with the 3.8-liter engine on both trim levels. If you looked and couldn't find it, rest assured that your LeSabre does have a positive crankcase ventilation valve. It's hiding under the manifold air pressure sensor.
Remove the fuel injector sight shield off the top of the engine, then take off the MAP sensor on the front of the upper intake manifold. You'll need a 5/8-inch socket to press down and turn the PCV access cover, but once you get the cover off, you'll see the PCV valve in the manifold. Make sure the O-ring comes out with the old valve. Replace the O-ring when you install the new PCV valve.
