I know this has probably been discussed many many times before, but I am still having trouble with deciding what oil to use in my OLD vehicles. I have a 1980 chevy with a 350 C.I. with about 160k, and never any major work --A 1965 ford with a 200 C.I. 6 cylinder, has been overhauled about 10k ago--- and a 1950 ford with the 239 C.I. flathead v/8. and it has been overhauled about 5k ago. My main concern is the ZDDP content of the oil. I can not decide if they need more than the amount in the newest SN oils, or if since they are all well broken in stock engines, that the modern oils are sufficient. If I need more, I will probably use QS Defy.But they never seem to put that on sale around here anyway, so am wondering if other oils would give plenty of protection to the cams, and I would have more choices. For instance Mennards right now has QS full syn. on sale after rebate, for $1.99/qt.