I've been going through the same thought process. This isn't the first time it has happened. The first time, mounting studs were loose. The second time, lifter guts blew apart and now this. When I did the lifters, I compared all the pushrods and they're all the same length. I find it really odd it happens only on those 2 cylinders. I'm wondering if those 2 rocker arms aren't shimmed correctly and have the pushrod at a slight angle which lets the pushrod walk off the lifter.
