Great thread, one that I will need to reread a few times. Experience is speaking here. I'm not sure consensus was had, though I do believe the usage of a 0W-40 oil in this engine would make me sleep better.
Hardening and or general metallurgy does appear to be an issue; perhaps it's an industry-wide quality issue?
Come to think of it, what were the thoughts or reasons behind the applicable MS oil spec(s) surrounding the 6.4L HD truck and possibly the SRT engines? The spec I'm speaking of calls for rated 0W-40 oil. Was it MOFT, besides others? Thanks.
All of the SRT engines have called for 0w-40 since the beginning. Was originally M1 0w-40, then the SOPUS watered down one after the Fiat takeover. The 6.4L HD engine appeared to continue that trend, calling for the same SRT 0w-40 for whatever reason.
With everybody and their grandmother going overhead cam, there does seem to be some QC issues with pushrod components. Both GM and FCA (previously DC) have had lifter issues and it appears that FCA had cam core issues, which GM has avoided by using billet cores rather than SADI.
The issue with SADI cores overall has been an intermittent problem since the late 90's from what I recall. Once the industry began moving away from pushrods, it became quite difficult to get quality cores, the production of which I believe was off-shored. This was particularly problematic for flat tappet applications (which use SADI cores) and was one of the reason for the "WE NEED MORE ZINC!" response to failures, which, in reality, didn't solve anything. Even stock replacement camshafts, for which normal levels of ZDDP were more than sufficient, were suffering failures. QC issues from the main aftermarket brands were widespread which had to do with the quality of the cores they were receiving.
This really isn't "new". GM had a rash of issues with SADI flat tappet cores during I believe the early 80's? Stock broomstick cams would lose lobes and camshaft replacement was common. Ford and Dodge didn't have the same problem, likely due to using a different supplier.