Did you ever find out about the content of WD-40?  I'm still curious. 
Petroleum based or not, it will dissolve all kinds of stains, etc. you
can't deal with otherwise - tar on feet, shoes, clothing, the superglue
they use to put price tags on merchandise, etc.  I try lighter fluid
first, and when that doesn't work, out comes the WD-40.  
 
And I maintain that it has not yellowed on my shells in 15 years I've
been using it.  Also, it seems to repel dust - not like oils, which
attract dust, have to be washed and re-oiled.
 
When we lived on the beach, tar occasionally washed up.  Inevitably, my
grandchildren got it on their brand new bathing suits. A spray of WD-40,
into the washing machine and all traces were gone.
 
Sylvia in Alabama
 
Kim C. Hutsell wrote:
> 
> Sylvia,
> 
> My landlord is one of the people who helped develop WD-40 here in San
> Diego during WWII.  I'll see what information I can get from him
> concerning its content.
> 
> Best regards,
> 
> Kim Hutsell
> Field Research, Marine Malacology
> San Diego
> 
> Sylvia in Alabama wrote:
> >
> > I have a question and an old issue to rehash.
> >
> > Question:  to those in Florida's "fire zone" which direction is the wind
> > blowing today?  (I want to know about the smoke in the Panhandle, if it
> > is coming from the southeast).
> >
> > Old Issue:  I am still a staunch believer in WD-40 for shells.  Someone
> > shot me down, saying it was a petroleum product and would eventually
> > cause the shells to yellow.  How do you know it is a petroleum product?
> > It doesn't say so on the can.  I was always under the impression (and
> > still am) that is it silicone, a combination of the element silicon and
> > oxygen, and a carrier to make it into a spray-on form.
> >
> > If it is a petroleum product, then why would it yellow and not the
> > petroleum products cited to use, such as mineral and baby oils?  Why
> > doesn't lighter fluid (another petroleum product) cause them to yellow?
> >
> > I started using WD-40 15-20 years ago, when I first heard about silicone
> > oil and it wasn't readily available.  I have not seen it adversely
> > affect my shells in any manner.
> >
> > When silicone oil became available I tried both, have both, and prefer
> > the WD-40 because it dries faster and is easier to use when you have
> > only one shell to do.  I've never had to redo a shell I've done with
> > WD-40.  Dust, smoke, and grime do not stick to it.  I can dust the
> > shells with my hair dryer if I prefer.  Once or twice, I have rinsed
> > them under cool water and wiped them dry, but couldn't tell that it made
> > a difference.
> >
> > And - what is silicon oil (see my dictionary definitions below)?  Isn't
> > it a compound of the element silicon, and some kind of oil?  What
> > amorphous states other than crystalline does silicon occur?  What oil?
> > Is the oil not petroleum based?  Is it vegetable based? Or is it pure
> > silicon liquefied under heat or pressure?
> >
> > OK, all you Ph.D's, chemistry majors, and museum curators:  Tell me why
> > I'm wrong, not just that WD-40 shouldn't be used because it is a
> > petroleum by-product.  Prove to me that it is, and prove to me that
> > silicone oil isn't.
> >
> > Sylvia Edwards
> > Huntsville, AL
> > -----------------------
> > sil·i·cone, n. Chem.
> > any of a number of polymers containing alternate silicon and oxygen
> > atoms, as (–Si–O–Si–O–)n, whose properties are determined by the organic
> > groups attached to the silicon atoms, and that are fluid, resinous,
> > rubbery, extremely stable in high temperatures, and water-repellent:
> > used as adhesives, lubricants, and hydraulic oils and in electrical
> > insulation, cosmetics, etc.
> >
> > sil·i·con, n. Chem.
> > a nonmetallic element, having amorphous and crystalline forms, occurring
> > in a combined state in minerals and rocks and constituting more than one
> > fourth of the earth's crust: used in steelmaking, alloys, etc. Symbol:
> > Si; at. wt.: 28.086; at. no.: 14; sp. gr.: 2.4 at 20°C.