Do they mix?

[Coot]

What bad experiences have you had with WD 40?

I have had WD 40 dry out leaving a sticky residue that gummed up delicate parts (HO couplers, modern gun internals, etc). WD 40 may be great for its designed water displacement uses and ok as a (coarse mechanism) lube when fresh, but there are much better lubricant and rust preventative products that are designed for those purposes.