From what I have read in the new Vintage Truck that there has been several cam failures (in rebuilt older mtrs) because of the lack of ZDDP (zinc dialkl dithiophosphate) in the oils being made today & believe it or not they are recommending Diesel oils in the older flat tappet mtrs. Can't tell you much more other then some of the rebuilders recommended it also & the author did some research on it. There is a 2 page write up in the magizine talking about it so you may want to try to find the magizine or maybe someone can ask Vintage truck if we can post that Tech Tip here on the bolt....