u/Affectionate-Milk593

I replaced my radiator with a Nissens radiator and this one has a cap. I’m struggling to find a cap that actually fits. It keeps leaking past the ones I’ve tried. I’ve tried 3 different ones that are “supposed” to fit. The place I bought it just say to use the original one but my original radiator didn’t have one because it was a sealed unit. Does anyone know what I can do? Can I plug it? Is there a radiator cap that people know fit? Any help would be appreciated.