The one at the Space & Rocket Center in Huntsville has been stored outside so it wasn't in good shape.
Displayed outdoors and on its side since 1969, the rocket was exhibiting widespread paint failure, moisture infiltration, an overall accumulation of atmospheric and biological soiling, and corrosion of its complex system of metal alloys, including aluminum. Non-metal materials such as polyurethane foam, various types of plastics including Tedlar®, phenolic resin, and fiberglass composites, had significantly deteriorated. The spacecraft portion of the Saturn V display (Lunar Adapter, Service Module, Command Module and Launch Escape System) were full scale 1970s era mock-ups constructed of sheet aluminum and fiberglass. The Command Module, constructed almost completely out of plywood and fiberglass, was is very poor condition
The others have been indoors so should be a bit better. The Huntsville rocket was incomplete. It's been restored from the above condition, but that's to 'museum exhibit' state, not 'functional rocket' state.
They'd need significant amount of work to be usable again:
- complete inspection of the metalwork, with replacement of any corroded parts. That alone is years of work. To do an inspection to the standard you want for spaceflight, you may have to disassemble most of the rocket (to make sure you get to all the corners that become inaccessible after assembly).
- replacement of all seals and other materials that can deteriorate. This may include the wiring.
- replacement of all the electronics
- new turbopumps
- new LOX tanks, maybe (LOX reacts with lots of things, there's no way to guarantee the tanks are clean)
- the Huntsville one was missing its CM, SM an LEM, so they'd have to be built.
- other parts may have been cannibalized, no way to know until you strip the rocket.
IOW, you're better off building new Saturn Vs.
I'm tempted to compare it to building vs restoring cars. A thorough restoration can easily take a year. Handbuilt cars are built in weeks...