Hi, Tom!
I can tell you one success story for WD-40. A number of years ago, I obtained one of the pinkish Conus pertusus
(excuse the spelling - I can't find this one in the book right now) from the Phiullipines. I kept it in complete darkness, and it faded hopelessly in less than a year. On the recommendation of a dealer, I got another one and used WD-40 on it. It is still bright and many years old.
Cordially,
Linda