so i've read the book that discusses at length benzoyl peroxide for use in vinyl dolls - "The Definitive Book on the Care and Preservation of Vinyl Dolls and Action Figures" by Nicholas Hill. this book is cited on the pony preservation project and came out in the late 90s, so i'd assume what happened was doll collectors got ahold of this book and pony collectors tried out the methods inside to varying degrees of success. i can't go and check it, since i had to get it from interlibrary loan, but as memory serves the benzoyl peroxide was only used on light skintone colored plastics that hadn't been colored with any type of dye; and it's advised not to use it on dolls with a darker skintone, or on painted areas and clothes. from what i've read on doll forums and reddit the method continues to be used without any evident problems on light toned dolls, at least as of now, so it's probably ok for use on the dolls that are known to not have any adverse reactions. if you can't find any info on whether benzoyl is safe for your particular doll though, i wouldn't risk it.