340 Lifter failure, now what

gzig5 said
From what I gather, that can be one issue. There may be others and hydraulics have more opportunities than solids regarding their internal components.

Yes, i do know that they need that convex base for the rotation feature. If it is flat it wont work properly. I used to touch the bases of two lifters together and see if they "rock" but that is an inaccurate way to check.