I picked up some oil based paints for models the other day (little tiny bottles), matching colors of a few REOs. Haven't tried it yet but you will have to do it like you do with small scratches and nicks in car paint, with hardly any paint on tiny point of brush so that it just flows into the scratch without coming over the edge. Very few of my metal REOs have anything but a nic or two, so I'll definitely be using my magnifying headset and trimming the brush down to just a few hairs. Also, paint thinner on hand to remove and redo if too much paint into dings. The worst one I have is a black Mini that DH carried the longest of any. Don't know why but he's dropping them less now, except for them sliding out from his lap when he gets up from recliner, onto vinyl, but hard commercial, tile. Worst that happens is a broken CV Pawn.
I still haven't applied the gadget "skins" to the metal REOs. That should protect except for a few places/edges. The textured vinyl looks really cool, too. First ones to be done will be the pristine tumbled Mini and Grand and then the Polished Mini and Grand, mostly for fingerprints, on the polished, as all but the deepest gouges can be polished out of them.
I got some extra colors, including white, model paint to adjust colors if needed but there were a whole bunch of already mixed colors that look to be very close to the REOs. Remember to start with a very clean surface and let the paint just flow into the "ding."
Alice