[Phlogiston]

No. The WD-40 will evaporate - mostly. What is left will not protect for long but it will make replating or painting difficult.

If you just have small spots, use the jelly carefully since it is very good at removing plating which will make future rusty spots bigger. Then get some silver paint, the old stuff has a greenish tint - NOT CHROME (paint) - and wipe it on with a small brush (I use my finger) like stain, only on the small spot. Blend a little (easier with finger) and try to leave as much of the original plating in place as possible. Clean off finger.

If your chassis is SO rusty as to need to be completely painted, find another chassis. If the chassis was originally painted - repaint it.

Caswell sells brush-on plating kits, mostly for copper and nickel. These can be used to replate small spots and work very well - yes you can sometimes tell where the spot was fixed. I use this method to plate the solder joints on re-stuffed Mershon caps. Works great. Just used the nickel brush to do a small spot on the AK 82 chassis I was working on.

I think that a lot of early Philco chassis were zinc plated - turns dark grey. If you are going to touch up one of these silver isn't the right color. I do have some "cast" color in a spray can. It is a better match. Though I have had it for 15 years or so, it is probably still available at car parts stores. (That is cast - as in cast iron)