I've had a broken F4 in my drawer for a few years. It was a minor problem but would require more than I could buy another used body for. I wish now I'd documented the teardown. I was truly impressed by how much stuff Nikon got in that body. Real metal gears, tons of electronics, springs upon springs. I've taken other camera apart but this on was the best ever. We are all amazed at the $6,0000 cost of a new D4 but I'd guess if Nikon wanted to put the F4 back into production I'd cost $10,000 to build one today. I'd use this camera for close to 20 years never had it CLA'd and the insides were clean. I'm now planning mount the parts on a board and frame them.
To take it completely apart to the last screw took 5 hours. That included having to force a few parts to speed it up.
God I'm a sick puppy....