Problem is, it won't leak plain water but put AFZ in it and then it leaks. Antifreeze is slicker than plain water and will leak where water doesn't. Seen it a hundred times.
They took the zinc out of STP a long time ago. Against the law to use it since sold for use in on highway vehicles. You can still get zinc in some oils like specialty race since they will state on side of container not for highway use. And why you pay so much for that disclaimer now.
I used either straight 30 (winter) or 40 weight (summer) for many years in my Mustang II with 2.3, it never once knocked on startup. I hear all the jazz about using lightweight oils on cold start to prevent 'dry start' but a misconception, only two or three true dry starts and the engine tears up pretty fast. My view is that the thinner oil also drains out of bearings faster since capillary action that keeps it in place drops with thinner oil weight. And after pulling down many engines that did not run for years prior to teardown, you find oil around the bearings when torn down. I even run heavier weight in my late model Ford zetecs, 30 weight forever until Walmart quit carrying it, now 10-40, I don't put the suggested 5-20 in ANYTHING. 3 cars running like that now and can't tear them up. I have actually fixed startup higher mileage knock by switching others cars and trucks to heavier weight oil before, chew that one over for a bit. The thicker oil does not backdrain out as much before cooldown, they don't mention that at all in the oil ads do they???
I was told running too heavy a weight oil in my variable cam timing would mess it up, 180K now and still no trouble at all with it. LOL.
I'm in Texas, you can't get away with that up north, it gets too cold. I can start a car here even at 5 degrees, it rarely gets colder than that.
You can look at BITOG two ways, they know everything or some of them are quite full of crap. Doesn't matter if they ARE engineers, once you see things yourself real world you can find fault with some of their ideas too. I used to know some engineers at Vought Aerospace, some of those guys were flat crazy and their ideas were as well. We built engines for them, they could not keep them together.