Broken or Cracked Head Gasket?

What is your question?

A couple weeks ago my 2012 Lincoln MKZ overheated while idle at a stop light. I pulled over, parked the car and opened the hood to check and when I opened the coolant it hissed and overflowed a dark green and oily liquid. I assumed a head gasket issue and towed it to a mechanic the following morning who couldn’t find anything wrong, no leaks, no over heating...nothing. It’s driven the last couple weeks with no issues until last night when I noticed it was leaking oil, though the oil has a dark green tint similar to what spilled out of the coolant a few weeks ago. Could this be an internal leak that got missed or am I looking at a head gasket. The liquid leaking from my car looks like oil but when you wipe it up it has a green tint...I know coolant and oil don’t mix but they seem to appear mixed! What the heck is going on! They pressure tested and found nothing, so I’m at a loss as to what’s happening. I should mention the mechanic told me that was the normal coolant type for my car