Here's what I did a few years back on a head that I bought used and needed repainting.I told the paint guy not to paint the floor because it was cruddy and rusty.He accidently painted it anyway.So I painted over the red with graphite paint,and it buffed up like glass after the first round in the field.Since that paint is soft,it started wearing through gradually to the red,and then gradually through to the metal.Shined up each layer as it wore through. In your case,I would coat with oil the areas you don't want a heavy coat of paint to stick to,paint everything,and the floor area will take care of itself next harvest.