Not sure if this is the right group to ask this in, but has anyone used RevX additive? Recently I starting hearing from some very knowledgeable guys that are swearing by it. It's expensive, to the tune of $32/4oz. I've put it into a 2011 Ford F150 3.5 ecoboost with 251,000k miles that makes a bunch of racket on cold starts. Sounds like really loud lifters knocking. This stuff made it silent about 95% of the time, but just wondered if anyone else has tried it...