If you do have holes in the bottom of the intake that penetrate the plenum, it will suck oil from the lifter valley. I'd certainly check that out and would bet this is your problem.

Regarding the leak down test; Did you actually turn off the incoming air to see how long each cylinder would hold pressure? If the cylinders will hold pressure, and based upon the compression readings you describe, you probably do not have a ring problem - but it is also possible that excessive oil in the chambers will help seal the pistons against the cylinder walls and hide a worn ring problem.