I managed to clean off all the dirt on one of these. Used both Goo Gone and Goof Off. Goo Gone took a little work and couldn't quite get all the recessed detail, but does work. Goof Off was very strong and took the dirt off quickly, but you have to be extra careful to not touch any of the details you don't want to come off - especially the helmet. If there was a product in between, it'd be perfect.