I use "Gunk" Pro Series Brake Cleaner with no issues. Caution should always be used when stocks and other pieces are involved. Nothing cleans a dirty FAL better than a can of brake cleaner
I started using this due to a friend insisting that it would work. I was concerned, but I figured I would give it a try. It has work perfectly since I started using it, and the bonus is my father owns a car dealership so from time to time I go down and score a can or two. Nothing beats the price, free.
You will go through it pretty quick though, as it comes out like a gushing gyzer. (No idea how to spell gyzer)