Automatic Transmission Fluid is a powerful detergent that is not harmful to most things even plastics, its excellent for cleaning basically anything that has tough burned on grease or fouling like valve covers or carbon fouling in guns.
Just let it sit and it softens and lifts stains and grease off of metal, plastic ,and dark fabric and can bring old baking sheets back to life (just clean them really well), it does have red die so will stain light fabric and hilariously light hair.
ATF works great for preventing the buildup of really tough fouling especially in the bolt carrier of the AR-15 I use it to clean the bolt and I leave a very light film on it.
Fouling just wipes off with a rag even when I am lazy and don't clean the gun right away.
Buy a quart of Mobil 1 synthetic ATF for like $10 and for the cost and the volume compared to other gun cleaners its a lifetime supply for basically nothing.