I actually found a type of WD-40 spray lubricant that's marketed as safe for metal, plastic, and rubber. I haven't read the "Ingredient" list, but it seems legit. Here's a link (not affiliate) https://www.amazon.c...t/dp/B07WXMX3HQ
I've got no idea if it'll actually destroy your foam flinger or not. I just know it exists and have used it on metal.