WD40 stands for "water dispersant", which is its primary use. 3-in-1 is best
as a lubricating oil. Plus gas is best for penetrating.

I want some spray oil to use as a very light oil.
Not for use as a penetrating oil.
More as a waterproofing oil.

I'd go for WD40, although if you want it to last some time, you might be
better off with a grease, rather than light oil.

Also as a solvent for the glue on adhesive labels.

I don't know about that.

Christian.