Just bought a 2004 and 2005 Sonata GLS, and have a 2007 Santa Fe SE purchased new. The 04 has 120000K, and I don't know the maintenance history. I pulled the front three plugs, and they had a gap of aprox. .0075. I knew I would have to change them, but I also heard that the rear ones were very difficult. My local Hyundai wanted almost $500.00 to do it. I found this site on one of the threads: Hyundai Santa Fe Spark Plug replacement on a V6 Cyl
and went at it. It took me just a little over an hour, and went very smooth. By the way, I couldn't check the gap on the rear plugs because there was nothing to check, they were completely burnt up. This weekend I am doing my 2005, and by the time I get to my 07, I should be an expert, plus save a ton of money. FYI, I used NGK Laser Iridiums.