Useless information about that "oil vent tube":
In Shop Manuals, the tube is called a crankcase ventilator pipe
It is also more commonly called a road draft tube
from the Wikipedia - PCV
"Prior to the early 1960s, automobile petrol engines vented combustion gases directly to the atmosphere through a simple vent tube. Frequently, this consisted of a pipe (the "road draft tube") that extended out from the crankcase down to the bottom of the engine compartment. The bottom of the pipe was open to the atmosphere, and was placed such that when the car was in motion a slight vacuum would be hopefully obtained, helping to extract combustion gases as they collected in the crankcase. The oil mist would also be discharged, resulting in an oily film being deposited in the middle of each travel lane on heavily-used roads. The system was not positive though, as gases could travel both ways, or not move at all, dependent on conditions. Most modern diesel engines still use this type of system to dispose of crankcase fumes. During World War II however, a different type of crankcase ventilation had to be invented to allow tank engines to operate during deep fording operations, where the normal draft tube ventilator would have allowed water to enter the crankcase and destroy the engine. The PCV system and its control valve were invented to meet this need, but the need for it on automobiles was not recognized."
GM introduced a PCV system for truck engines in 1948 when it started selling Forward Control Chassis models to be made into delivery vans. There was little road draft for a door-to-door delivery van (milk, bread, etc) driving slowly and stopping at every house in a neighborhood.
