Standard failure for these design of roller lifter....
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Dogbone style roller lifter guides like the Jesel units are much stronger...
Lifter bore misalignment is the usual root cause...or excessive cam end float....
It only takes one impact of a roller lifter body against a next in line cam lobe and the lifter rotates and rips the pin out of the body...instant failure...
Full rebuild...all oil gallery plugs out and full gallery clean....
Check the valve spring pressures....note...the roller rockers will most likely be ready to fail as well from the contamination...
Seriously...look at the Jesel style lifter retainers....
Take it slow and keep us informed...