If it has been driven 5k miles I doubt it was a probelm related to PTV clearance, it would have happened right away. Still check for a bent valve just to be sure....
Overtightened nut sounds probable....
maybe your spring pressures are too stiff for those rockers to handle, check that and call Hughes and see if they are within spec.
Check everything closely.....if all looks good, I guess Id just replace that single rocker.
Im no expert...Im usually just asking questions and learning as I go.... most people on this forum may be more knowledgeable, but if it was my engine I guess that would be my game plan.
