wd40

It won't hurt anything but it does leave a slight gummy residue.

Iv'e heard WD40 is more or less kerosene with perfume, don't know if that's true or not. But on a tractor keep in mind it will act as a dirt trap. Maybe put some on a rag and rub it onto things you don't want to rust. Silicone or vasoline would be good for anything rubber, the Chinese rubber is absolute junk and dry rots quickly.

Personally, the only thing I use WD4j0 for is removing paint from my hands.  It is a crappy lubricant, equally crappy preservative and truly horrible penetrating oil.  It does have really good name recognition though, so it sells a lot.

The stuff attracts dirt like a magnet and then it traps water.  Bad idea, in my view.  As Tinbender noted, Vaseline is a better rust preventative and is basically a very high-grade cosmoline.  It also holds dirt, but the film strength is so much better no water penetrates it. 

Water (moisture) is heavier that oil, any kind. WD-40 is a petroleum based product. Any protection against moisture is short lived after the propellant evaporates.

ASTM has procedures for testing metal preservatives.

I wouldn't use WD-40. If you're serious about it use Cosmoline or Lubriplate.

Along the same lines,  What is a good protectorant to use on battery posts? Brand name , please.     Thanks, BG

Permatex makes a good product, a little spendy but I think they all are. I just use grease on most of my vehicles.

For batteries I use CRC Tech Grade Battery Cleaner, and CRC Tech Grade Battery terminal and Post Protector.

For metal protection I use ZEP Iron Clad. I use it on all exposed metal that I don’t want to rust including hydraulic rams that are laid up for long periods.