Both. I used to clean cosmoline off of VW's . They came coated with it for shipping overseas. I used a steam sprayer with kerosene injected into the sprayer. Worked great for big job's like cars.Mineral spirits or hot boiling water?
There ya go...I cleaned up about 30 M1 carbines mags that had been stored for 50 years. The cosmoline was thick and there was lots of it. I bought a gallon of mineral spirits and soaked them over night. Blew everything out with compressed air the next day. Clean as a whistle.
WD40, rag, toothbrush. Then lube it with something better after you clean all that gunk off.
Someone over at Gunboards (IIRC) named it Sticky-Snot cosmoline.