• The head mating surface should have been verified for flatness.
• The mating surfaces needed to be thoroughly clean at the time of coupling. Material from the head's being set on a table or floor could have been transferred to its seam from those surfaces then have affected sealing.
• A lightly lubricated screw will exert more force at a given torque value than a clean, dry screw—approximately 10–15% greater force.
• If close attention isn't paid during the procedure, the wrong torque scale can be used. If the Nm scale were used mistakenly, setting it at 33 would result in lubricated screws being tightened to approximately 26—28 ft. lbs. This can happen from distraction and/or from unfamiliarity with the tool.
• If the head has been dropped somewhere along the line, a crack in the head could have been created.
• The combination pump seals could be faulty.
A check with the oil pan removed while filling the radiator with coolant could help be helpful determining the source of leaks. The oil pan and the oil pickup screen should be cleaned because of this contamination regardless.
What seems to have been asserted by you is that approximately two ounces of coolant found their way from the coolant reservoir into the oil pan during eight days of idleness. That seems an unusual scenario given the relationship of the reservoir coolant to the radiator in a stone cold engine.
The tests for combustion gas in coolant, and leak down tests are relatively uncomplicated.