I'm amazed people still use oil stones, MarcL. Water stones make so much less mess.
I rarely sharpen my chaveta. After all, it cuts more by crushing than it does by slicing. And the angle on it is so obstuse anyways. I agree a few strokes from a fine file ought to do the trick. But the coarse side of a small two sided carborundum stone, the kind that fits in your hand, works for me. Has a black fine side and a gray coarse side. Sold as an oil stone, but if you never oil them, you can use them with water. Good thing you got me thinking, cause mine has been worn hopelessly swaybacked, & I've been meaning to get a replacement for a long time. I'll just tap Amazon right now.
There, done. Scored me this:
I have used a diamond stone as well... industrial diamond dust bonded to a smooth piece of steel. But the klepto-ghost who wanders round our house snatched that tool from me a while back. I have a folding diamond stone I take camping. It's got a plastic handle it folds into. I have tried that. Like the plain two sided deal better.
Don't stress over getting it sharp. You can cut wrapper with a fingernail, after all. Done that by accident many times. So truly sharp is hardly required.