This technical report evaluates custom high-temperature oil-resistant silicone rubber engine bay seals for the 2026 automotive landscape. It analyzes critical failure modes like compression set and thermal hardening caused by extreme thermal cycling ($>$180°C) and synthetic lubricants. The guide establishes **Fluorosilicone (FVMQ)** as the industrial baseline, comparing it to standard VMQ using ASTM D2000 metrics for oil swell ($<$5%) and dimensional stability. Key procurement strategies focus on wholesale automotive rubber gaskets compliant with IATF 16949, UL 94-V0, and IPC-WHMA-A-620 standards to ensure "fit-and-forget" reliability in turbo zones and high-performance electric drive units.