Seems the least harm here can come from a check valve on the pressure side, not the vacuum side. Oil CANNOT leave the immersed suction side unless somehow air to replace the leaking oil can somehow gain entry, and a pressure side check would "check" both air and oil, regardless of loops, fittings, etc. How/where you can place a check valve on the pressure side for a BBM is above my pay grade.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
