Had an eruption of oil on my 81SD last December. After recovering from the panic attack I undertook a very carefull exam of where the oil came from and why so suddenly.
Turns out I had checked the oil and had left the dipstick out a 1/2 inch. There was enough blowby to pump oil out the dipstick holder there. Lost a qt in 40 miles. A real mess all over the left side of the engine.
Lesson learned is to push the dipstick in tight several times. Not worth the mess to let it happen again.