I put in Slick50 the first oilchange I did on the 67 2 years ago and almost immediately developed a knock. I changed oil again and went back to the QuakerState 10-40 that my father-in-law used for 30 years and noise went away. One of my workmates later told me that Slick50 has lawsuits against it for ruined engines. Apparently it contains parrafin and had a propensity for clogging things in some cases. Dave 67 Haze Green sedan Covington, Wa.