It would have helped to tell us what sort of toy engine this is.
Your question makes it sound like a child's toy train. The engines you sell are very different: diesel and glow plug engines for R/C controlled models, listed in the petrol/nitro category.
Anything with a previously filled fuel tank included could certainly be excluded. (Even previously filled petrol lighters are prohibited.) eBay's restrictions interface with restrictions on the carriage of hazardous materials, so sometimes this can depend upon the intended delivery mode or the t&c of the intended carrier.