I'll add that at least in the case of the Rocketdyne F1 Engine (those five huge engines at the bottom of the Saturn V) in addition to hardware, there are either missing or never-existed notes and personal knowledge on a large number of small details that would be helpful to build a new F-1 with the same reliability as those of the Apollo era, as discussed in the Curious Droid video Why Can't we Remake the Rocketdyne F1 Engine?.

I'll add that at least in the case of the Rocketdyne F1 Engine (those five huge engines at the bottom of the Saturn V) there seems to be some instances of either missing or never-existed notes and personal knowledge on a large number of small details on the fabrication process (how to assemble, fit, weld, etc...) that would be helpful to build a new F-1 as discussed in the Curious Droid video Why Can't we Remake the Rocketdyne F1 Engine?, also viewable below.