DIAGNOSIS The bar oil cap vent is clogged or the O-ring seal is damaged. Pressure builds and forces oil out.
FIX Clean the small vent hole in the center of the oil cap with a pin. Check the black O-ring on the cap for cracks or nicks. Replace the cap if damaged.
IF THAT DIDN'T WORK The oil tank itself may have a hairline crack, often near the fill neck. Inspect it closely in good light.
HEADS UP Only use bar and chain oil. Motor oil is too thin and will leak more. Store the saw on its side, not upright.