I could use some experienced advice. Has anyone done the oil analysis Bob Is The Oil Guy recommends? If so, who did you use, what did it cost, and was it worth it? I suspect my old pathfinder has a leaky head gasket, and I think that an oil analysis will uncover of that is the case or not. If it is the head gasket, any ideas what the repair will run me? I was blessed with good looks, not mechanical aptitude, so I will have to pay to have it done. What are your thoughts on the effectiveness of thisapproach to see if the head gasket is a problem? Thanks.