Originally Posted by Speedy

A leak down test is going to beyond the average person's mechanical ability. The head gasket test is easy peasy and will tell you the same thing in seconds.

I personally wouldn't tell Nissan I had tested anything. I'd test it to know for myself then drop the car off and tell them the head gasket blew again and let them do their own test, likely the same one.

Bubbles in the coolant over flow tank at idle is another sign of HG failure BTW.

Let us know how the test turns out. I'm curious.