Where do engines ‘throw oil’ from?

This is an example, meant as a general guide for the breather tube exhausting somewhere away from the cockpit. Compare and contrast the two airframes. The nearer has quite the trail from the breather. This usually indicates leaky rings on the pistons, pressurizing the crankcase.

The B-25 Mitchell carried 31 gallons of oil for both engines. New engines in perfect shape would burn a gallon of oil an hour. This information came from a Army Air Corps mechanic whose job it was to receive B-25s from the factory somewhere down in Texas (Sheppard?). I also remember seeing the Collins Foundation B-17 parked at a local airport and people were concerned that oil was leaking. My great uncle (a B-25 top turret gunner) was in turn amused by their concern. He told me, "I only got worried when they ran out of oil to leak." I asked him if that ever happened to his aircraft and he said, "I looked out at the starboard engine and saw a piston chugging up and down, with nothing surrounding it." THEN I was worried!"

Any place that has oil can leak oil. A tiny leak or drip would "spray" when it is in a 200-400 mph. slip stream. I am sure that one couldn't even narrow it down to a handful of causes for any one such incident. The oil coolers themselves probably have more than dozen points of possible leaks. (the oil tank for a P-51 was right on the other side of the firewall).