Additive manufacturing (AM) enables the rapid fabrication of complex geometries that are unattainable through conventional manufacturing methods, such as computer numeric control (CNC) machining. Despite widespread potential for adoption across industries, including aerospace, biomedical, automotive, and architecture, AM still faces critical design challenges and expertise bottlenecks. This study examines how immersive virtual reality (VR) can facilitate the capture of expert knowledge in design for additive manufacturing (DfAM), where computer-aided design (CAD) software remains pivotal in addressing these complexities. However, traditional CAD systems pose limitations in intuitively exploring novel designs or complex geometrical contexts. CAD software remains pivotal in addressing these complexities, yet traditional CAD systems pose limitations in intuitively exploring novel designs or complex geometrical contexts. We conducted an observational user study with nine AM experts using a custom-developed VR environment. Participants evaluated three CAD models of varying complexity, highlighting the effectiveness of VR for detailed inspection, spatial understanding, and manufacturability assessments. Results showed high usability, low cognitive load, and effective spatial exploration. Experts identified further improvements, including integrated scaling references, component-level inspections, and enhanced slicer software functionality. Our findings highlight the potential of VR to streamline AM workflows by intuitively capturing and applying critical manufacturing expertise.