Just replaced my head gasket (2nd time..) with the same issue.

If the rear main seal was leaking, you will find oil on the transmission bell-housing under the torque converter.

You need to wipe the area down completely, then start the car and watch carefully using a mirror. It should be obvious if its coming from the valve cover or the head gasket.
Look for oil on the block.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k