I think there is a check valve in "upper oil pan" below the oil drain-back tube. Try blowing thru the tube with your mouth. I feel something pop open under slight pressure like a valve. Yours could be clogged. However, I think you should get just faint oil if there is minimal blow-by past the rings, maybe a few ounces in a 100 mile drive. That is more likely your problem. See you-tube videos to judge your blow-by. If so, there is no easy cure unless you believe the magic bottles at auto parts. The magic is how they separate desperate owners from their money.