The AF of my 60 AFS simply stopped working one day so I simply bought a replacement. It was then several years old - bought it right after it came out. My even older 105 AFS still works as new. I do not have an F4 to do the Rockwell test described above but am a bit surprised as the F4 has a very old AF system. I have used both AFS lenses housed under water without major issues for years. Though I have used a D3X and not a D3 per Rockwell.