I picked up a Yamaha F-345 from a colleague for $50. I had been knocked at the nut, so it had a chunk out of the nut at the high E (first string). The folks at Yamaha were amazing, and shipped me out a new nut and a spare for something like $12 all up.
Replacing the nut simply took some sanding off the bottom of the nut to get it to the height of the original and a bit of resorcinol glue to hold it lightly in place.
Lastly, since the belly below the bridge was somewhat raised (it may have been stored somewhere damp under higher string tension), I ended up flattening that belly substantially by placing it under pressure using some clamps and a flat hardwood board, while “humidifying” the interior with a wet sponge in a low cream cheese tub to “retrain” the wood. I used “Press and Seal” to seal up the sound hole, and left it like that for about a week.to let the humidity creep into the wood from the inside only. Finally, I opened the sound hole, removed the cream cheese tub and the sponge, then left it to dry out still under pressure. The result is the belly is substantially flatter, the action is better since the bridge is lower, and it seems to have no negative impact on intonation, glue strength or anything else.
Wonderful guitar with a great ringing tone – this is a really enjoyable instrument! I believe the top on this model is Sycamore wood ply, which gives it a somewhat darker tone than spruce, but not as dark as cedar. It also shows that, thanks to Yamaha’s ability to design great sounding instruments, it’s entirely possible to create a truly exceptional-sounding acoustic guitar that has a laminate (plywood) soundboard.