2010 Mazda CX-9 AWD Automatic, 165k -Oil Leak, Mechanic can't find it.



I was recently on a road trip with my vehicle to Colorado & Utah (from Minnesota) and on the return journey I noticed a burning oil smell, smoke coming from the hood, and oil splashed around my engine bay. I took it to the only available mechanic in the area and he couldn't find the leak but said it was probably the valve cover (didn't have time to look further). To preface this, my valve cover was replaced back in MN a month ago during a routine check up. On the 1,500 mile trek back home I was constantly smelling burnt oil, seeing smoke, adding a little oil, and going through car washes.

Once I got home I took my car back to the MN mechanic that serviced the valve cover replacement. They spent the day looking at it and weren't able to find a leak. Any idea what could be wrong? When I spend 15 minutes on the highway I see symptoms but they couldn't? Seems odd to me.

What's also odd is that I don't have any check engine lights and when I drive it things run smoothly (always has before this incident). Thanks!