How do hydraulic flat tappet lifters fail?

Righty Tighty said
I think (I hope) we’ll find some answers when I pull the cam and lifters. Drained the oil today and it was very, very clean. I’m going to cut into the filter and see what it looks like, and check the rod and main bearings (at least a few) to ensure they’re in good shape.

When I pulled the valve cover, I saw the #1 intake pushrod shifted to the side. Here you can see the divot it made in the rocker. And yes, I have a new rocker to replace it! :lol:View attachment 1715614237

Interesting the old chicken or the egg deal, which failed first?
My money is on the lifter, it failed first. Although those rocker arms are dam hard and normally can take alot of abuse before leaving a mark like that, you may have a valve guide issue causing all this.
I no longer use hydraulic flat tappet or roller lifters because of the problems with them.
Did you check each and every lifter for surface crown before you installed them?