5D rusty strap holder

Any idea how to clean the rusty on the strap holder?

From my experience dealing with rust in other areas, I would suggest something like the following:
- Cover the rest of the camera body with painter's tape and a plastic bag.
- Use a little brass wire brush to remove as much of the surface rust as possible. Dust off the rust dust as best you can (blower or tack cloth)
- Use a Q-Tip to dab on a chemical converter such as Rust-Oleum brand Rust Reformer. It'll take a couple of days to dry.
- The end result will be a surface that looks like it has been painted matte black. Don't worry that it looks gooey white when you first apply it, that's normal.

I've done this for other things (automotive, household) but haven't done so on a camera.