I think it's pretty easy to do it yourself, with two cautions. Focus to the minimum distance, and you'll see three screws exposed on the barrel above the focus ring. Warning #1, the screws are JIS, so a Phillips #000 screwdriver almost fits but sometimes just ruins the screw without budging it. Remove those screws and the filter ring comes off like this:
Focus back to infinity. Just inside the focus ring and outside the front element, there are three screws that attach the focus ring to the rest of the lens. Warning #2, don't remove them. That puts the contact brush in danger as mentioned by wlachan. All you have to do is loosen them a bit until you can turn the focus ring without the lens actually changing focus. In your case, it sounds like it just needs to be turned a bit clockwise. If you have the lens mounted to a camera and the camera on its back in AF mode, the drive screw will help hold the lens elements in place while the focus ring turns. You can tighten one screw and check it before reassembly. When it works well enough for you, just tighten those three screws and reinstall the filter ring.
When I took the photo above, I noticed some dirt near the focus ring screws, and the somewhat exposed focus helix threads. Dirt can end up in there and cause uneven focus effort. So I removed the focus ring screws and pulled off the focus ring, bending the contact brush. It's not meant to come out that way, though that's how a manual focus lens comes apart. I had to take off the mount and aperture ring, three screws and separate the lens body, then reinstall the focus ring, bend the contact brush back and reinstall that, then put it all together. I took the oportunity to clean the lens and regrease the focus helix for better manual focus feel.
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