Oil in the intake manifold.
After major field over haul on a Continental 0300 we have oil running down inside of intake manifold. This oil is also very dark in color. There are only 2 routs this oil could originate, one would be from cylinder intake or traveling uphill from oil sump being that the intakes path runs through the oil sump via a duct incorporated in oil sump. During the first 40 minutes of the start up procedure the oil tem and pressure remained in the green. Any thoughts on this?