Now some vibes you will not be able to get at the contacts with a nail file or sand paper, this is were you can use a pencil. Take a piece of sand paper and tape it to the end of the pencil on the eraser end.
Now you can reach inside the vibe and use a twisting motion to clean the contacts.
This will also help with area's that the file will not reach.
**Side note, you can use the WD-40 inside the vibe as it will not harm the inner workings but it will leave an oily residue in the vibe. For some materials, this will not work; also, it may leak out and get on your skin or even worse, your bits. Please use your better judgment. **
After you have sanded the inside, tap/shake out all the dust/ rust whatnot
On most vibes there is contacts at the cap end, make sure to clean these off as well. Take your time and do a good job, the more rust you can take off the better.