A lot of people have cars that are "patina" and to prevent further rust use Marvel Mystery Oil (I think) or something similar on the sheet metal. If later you decide tho paint the car, how do you get that off? It seems like you would have to wash it off with gasoline or sand every inch of the car down to bare metal. I have one T I'll probably never paint but I have a Hudson that I probably will. I can't afford to paint it now but if it keeps on it will soon be from patina to solid rust. I don't want to create a nightmare for myself in the future trying to paint a car that I can't get the oil off of.

they have satin clear in a rattle can i think that would work to keep it preserved . check out the HAMB or jalopy journal too .Even cleaning good and a good coat of wax may work. i wiped some jasco over rusted areas and it seemed to leave a protective coating .

Boiled linseed oil with some mineral spirits mixed in to help it dry---50/50 is ok. protects, easy to touch up. I would imagine something like straight mineral spirits or lacquer thinner would take it off, but never had the need for that.

Marvel Mystery oil, WD-40 or whatever makes little difference when you finally paint a vehicle.
It will have to be stripped down to the bare metal and degreased - no matter what you use.
The only thing I would stay away from is silicon based stuff because it can be hard to remove.

Fred is spot on. ANY paint job prep will require constant degreasing throughout the various stages, regardless
of whether you applied something like linseed of MMO in the past. But more importantly is the second part about
silicons.

"silicon based stuff because it can be hard to remove."
Try near-impossible to remove, once it gets into the pores of the metal! Silicon is the darling of the "easy to apply" wax manufacturing folks, and the bane of painters everywhere.