Oil vs Epoxy coils.....

Try your local auto parts store.
40kV is sales hype. Peak secondary voltage is limited by 1. Spark gap in conjunction with combustion dynamics, or 2. Coil turns ratio times peak primary voltage, limited by collector to emmiter clamp voltage, whichever is least. The 40kV coil with high turns ratio, is less desirable for spark current due to impedance mismatch, and higher secondary resistance.

Buy whatever you want, I am only trying to provide information about specs, and how they relate to ignition performance.