Interestingly, it is somewhat hidden under the fuel injection sight shield. Here are the directions for replacing it. The pics correlate with the directions and show its location.
2003 Buick Regal V6-3.8L SC VIN 1
Vehicle Powertrain Management Emission Control Systems Positive Crankcase Ventilation Positive Crankcase Ventilation Valve Service and Repair Procedures
Positive Crankcase Ventilation (PCV) Valve Replacement (L67)
1. Remove the fuel injector sight shield.
2. While holding down the PCV valve access cover (1), remove the access cover bolts.
3. Remove the PCV valve access cover (1).
4. Remove the PCV valve (2), the spring, and the O-ring (3) from the supercharger.
1. Install the new O-ring (3), the spring and the PCV valve (2).
2. Install the PCV valve access cover (1).
Notice: Refer to Fastener Notice in Service Precautions.
3. While holding down on the PCV valve access cover, install the access cover bolts.
Tighten the bolts to 10 Nm (89 lb in).
4. Install the fuel injector sight shield.
I hope this helps. Let me know if you have other questions
Take care and God Bless,
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Thursday, February 4th, 2021 AT 6:26 PM