I have a 2010 Nissan Murano. Last summer (2018) I started smelling coolant when I get out of the vehicle or am at a drive thru with my window down. There is never any coolant on my garage floor. The coolant level has never gone down. I took it to Nissan when I received a notice for a free inspection. They said it is the head gasket and that the leak is so tiny that they recommend to just "monitor" it. They also quoted $4,000.00 to repair it. I took it to a mechanic that we have used for years and totally trust. He said he cannot find anything wrong with it. He also said they could not even smell a coolant odor. Not sure what to do at this point. It is my understanding that if you EVER smell coolant, there is a problem. Both places did pressure checks as well. Any recommendations?