In line. 6 oil in cooling system

Have this in line 6 cyl runs good but is getting oil in the cooling system pulled head did not see any thing that looked like it might be letting the oil into
Cooling system. Do the heads have a problem?

When pulling heads off of a vehicle I would recommend checking the heads and the block for flatness.
*Cylinder Head Flatness- 0.03 mm per 25 mm (0.001 in. per 1 in.) 0.05 mm per 152 mm (0.002 in. per 6 in.) MAX Flatness 0.20 mm - max for total length *Block Flatness- 0.03 mm per 25 mm 0.001 in. per 1 in. 0.05 mm per 152 mm 0.002 in. per 6 in. MAX Flatness- 0.20 mm (MAX) for total length 0.008 in. MAX) for total length