I suspect someone like Richard Haw can chime in with more expert advice, but I'd leave them alone, because grease can induce drag.
The aperture mechanisms in the lenses and converters I've taken apart over the years were not tightly assembled or preloaded, and never showed signs of grease, and I suspect that at most they had a tiny bit of some light oil, and even that was uncertain, but if present was probably something very light and special, like clock oil.