I've had to tear several 4.6s apart because of bad valve guides. One was on a lincoln and it only had 78,000 miles. On my old ford f150 with a 5.4L in it with less then 50,000 miles on it and the valve guides were going bad. I have heard from several other people that them valve guides are leaking.:bs hardly any issues ar all with seals or guides. if so i would of had to replace mine several times by now.