How do hydraulic flat tappet lifters fail?

512Stroker said
The janky ones had a lot of pressure on them causing the premature wear.

Considering I presoaked them, would that play into increasing the pressure they received?

dartfreak75 said
im no professional but a lifter should not be mushroomed to the point you can't get it out after 600 miles. That's some serious heat. Was the mushroom one on one of the bad lobes? I have seen carbon buildup stick a lifter in the bored before but not after 600 miles sounds like a oilling problem mixed with some bad geometry lol.
The way measured my preload was put the expandable pushrod in with the lifter and lobe in the valve closed position screw it up till it touches the rocker and takes the lash out. Then remove the rocker measure it and compare it to your pushrod it should be .02-.06 longer than the adjustable one

The mushroomed lifter is the exact lifter on the bad lobe. And when I say "mushroomed," I really mean that there's enough drag when I attempt to pull it out of the bore that I don't want to do it. I mean, I could yank it out if I wanted to, but I don't want to damage the bore when I do it. It's hard to tell, but maybe it's just a burr on the OD that's holding it up. All other lifters came out with zero effort, which is a plus.