I just replaced the plugs in my stock MKS earlier today. The car has just a tad under 50k miles. The coloration was good. Four of the six plugs were right at .040" and the other two were slightly above at around .042"-.043". I replaced them with Motorcraft SP534s gapped at .030". The car runs smooth, but I wasn't have any problems with the old plugs. I just wanted to see how they looked at around 50k miles.