Dropper lids tend to come apart easily. It's an oil so Dawn breaks it down. I pop the droppers from the lids and put them in the bottle, add a drop or two of Dawn. Add water halfway and shake gently. Then add water to the top and let sit for 24 hours. At that point, I open it up and use a tiny straw brush on the dropper. Put those upside down to dry so that all the water actually comes out. Then rinse and shake the bottle and lid until they are clear.
Just tossed a bunch of those. And gave another bunch to a family member. I hate tossing them but I can only use so many.