Decal cleaner

Does anyone have some suggestions on a product that can be used for cleaning the decals ? I’ve scoured around and can’t seem to find anything specifically made for decal cleaning? I’m thinking something that’s not aggressive in any way, that could permanently damage them. Maybe a vinyl cleaner ? Possibly something gentler, that could then be given a finishing wax coating when clean, such as Autoglym extra gloss protection. 

Last year I polished and waxed the van. Despite trying to be careful I guess I must have rubbed polish over the decals because there were swirl marks all over them and they looked quite dull, as if the surface sheen had been removed. Today I decided to have a go at fixing. My plan was to start with the least abrasive product. First up was Fenwicks black streak remover. Bingo! A little elbow grease and then a rinse and dry did the trick. Worth a try.