This is what I would do.
Call your local Nissan Dealer and ask what the hours are for the parts department.
Then go to or call the parts department a little before quitting time.
Ask the parts guy (or girl) if any of the mechanics do "side work" at home. If the answer is YES, then leave your contact info so they can call you back.
Go to your local part store after 6pm and ask the guys behind the counter who they would recommend that does stuff at night.
If you don't like my first two options, then you can go to another repair shop that has a store front business.
In any case, give them all of the details you have stated here.
The next person to work on it should "straight edge" the block and the head to rule out any future problems.
My knee-jerk reaction is the shop you went do did a poor job of replacing the head gasket. But I cannot say that with any certainty.
Monday, January 11th, 2010 AT 9:46 PM