I don't believe that's a good portrayal of the situation. I doubt that there's anything all that special about the actual Saturn V engines. Sure, maybe nobody remembers all of the engineering details about those particular engines, and it would be hard to reverse engineer them. But I'm pretty sure we would find it much easier to design and build new engines of similar spec today. SpaceX, Blue Origin, and several other new space companies don't seem to have had all that much trouble designing and manufacturing new, powerful rocket engines.

Ditto guidance systems. Why try to replicate something designed around the constraints of hardware that seems ancient by today's standards? No reason to think we couldn't build something new with equivalent or better features on modern hardware.