Well......dang.

[Wbulk]

With a minor leak in the combustion champer often times you will see it on the plug that will have a green tinge. You may also look for the recent thread covering a members issue with a head gasket leak from a stripped head bolt, that resulted in a small leak into the lifter valley. Since it appears you have a iron block it could be a small head gasket leak into the lifter valley.

[HighPlainsDrifter]

Hi,
I see you have ALuminum heads, they will expand at a different rate than the iron block so you need graphite head gaskets.There is a front orientation to them. Put thread sealer on the short-lower row of head bolts. Torque the head bolts to 70 ft/lbs. Torque the intake bolts to 18 ft lbs, run and let cool and retorque, do not over torque intake, it will leak.
Good luck,,
Perry.