[Will N]

I'd also add that as the engine wears and the clearances in the rear main increase, the amount of oil in the space between the bearing and crank increases, and the amount of oil working its way back to the slinger to drain back via the tube overwhelms the capacity of the tube. Adding to this is that if the bearing clearances have gone out of tolerance, it's also more than likely that the piston rings are worn, allowing blowby into the crankcase, increasing crankcase pressure which would work against the oil draining from the rear main via the tube. In fact, the oil drain tube would become a path to vent the crankcase pressure rather than a path to drain the oil.