if you do it over the clear coat, it'll be easier to smear and clean up
if you screw up. i found the easiest way to do subtle "oil"
smears is to put a line/spot on a clearcoated panel line and smear it
with a q-tip. you can kind of see the result in this picture
(there's a hatch partially covered up by the red star on the rear
fuselage) but it's not very clear since the plane's pretty
filthy-looking anyway.
