Radial piston engine oil leaks, DC-4 thru DC-7 and Constellations
Any offers on why these engines leaked so much? I'm talking about the copious oil you would always see over the wings of all the Douglas airplanes from DC-4 to DC-7 and the Constellations.
I think this was the reason Delta got fed up and painted dark blue a large swathe of wing behind each of the 4 engines cowlings to hide the oil.