Isuzu bulletin confirms oil use bull****

[89Vette]

I personally think there's more to the story than just oil drainback holes. There are people like me using molasses and doing fine and then there are plenty of people such as yourself who are doing fine with lightweight, low detergent oil. There's some other variable in this equation. Maybe more than one.

Like how often you change oil? That's a biggie. Longer intervals gives more time to accumlate debris in the oil -- and clog up the holes.

Where you drive. More rural areas with dirt roads lead to higher induction of dirt.

Mean temperature. Hotter areas might get to higher temps where more "ash" and carbon in the oil contributes to contamination.

Brand/Type of oil. Even if it's molasses, good molasses is better than cheap stuff.

Luck. How you drive it and what the exact clearances for each motor measure out. How the rings fit. Parts to have a tolerance with variance.