In order for oil to flow into the vacuum pump there has to be either air or piston blowby. If it doesn’t have either then there is no way for the oil to “move” into the pump. I use an electric vacuum pump and a blowby meter to check every engine before we start it on the dyno.

I can tell you that stock style BBM rear seal leaks air bad under a vacuum. The front does also but not as much. My 512 B-1, it had 6 inches at idle and 12 during a pull with lots of oil pouring into the vacuum pump. (a dyno pull takes longer then I am under power at the track). Knowing I had air going by the rear seal, I changed it out to a double lip design, went to 11 inches at idle and 17 during the pull and NO oil. (the engine was not unbolted from the dyno)

I would suggest finding a way to pull a vacuum on the engine without it running and using smoke or your hearing to find the air leaks.

One other thing, I don’t run a baffle inside my valve covers.

Joe