If you ship by sea, you can send almost anything you want in quantity with some extra paperwork. By air, flammables, explosives, corrosives and oxidizers are either prohibited outright or are permissible in small quantities with extra paperwork.
The courier companies coming here generally exclude anything they don't immediately recognize. It's up to you to research the iata regulations and file the appropriate paperwork. Even then, it took considerable time and effort to get EPS to change their initial determination - they don't want the hassles upon arrival in the DR.
I don't try to import dangerous goods anymore, it's not worth the extra fees and all the delays. These days I spend my time demonstrating how what I have bought is not classified a dangerous good and can fly without paperwork but alas all these companies are Dominican and decisions are made here not in Miami; Getting an MSDS sheet translated, apostiled, notarized and signed by the Pope is no guarantee anyone will read it let alone understand it as it relates to the shipping regulations.
In the past, printouts from the FedEx website dangerous goods shipping helper has proven effective as they all think they are just like FedEx.
So can it fly, depends on the ingredients, and how much you are shipping. Often special packaging is required for "dangerous" liquids. If Amazon ships the item by ground service, chances are it won't get on a plane in Miami. Even if Amazon sends it by air to Miami, no guarantee the courier will automatically do the same. EPS was really bad for that in the past and one of the reasons I don't use that service anymore.
I think your fuel additive will send the courier clerks towards a mental shutdown and your stress factor will quadruple at least.