Dexron and kerosene. 1:1 It's combustible but not flammable. Works as well as Dexron/Acetone, without the flammability. Diesel fuel used to be good, before it went low sulfur.
Or, electrolytic rust removal. Google it, it's fun. It reduces rust back into iron, without removing metal.
I've used straight Dexron as a rust pen, while at work-no kerosene available, and have used it to to remove rusted/galled spindle nuts.
You could always use Ed's Red. Google it. It's a good gun cleaning solvent containing kerosene, acetone, dexron, and mineral spirits in equal parts.
Every gun owner should make a batch of Ed's Red.
I've used brake cleaner and carb cleaner as penetrants, when I needed to removed rusted/gunked up lift chain anchor nuts. Gotta work fast with them. They evaporate quickly, but they also penetrate quickly.
Funny thing about Dexron. I use it to lube rusty lift chains at work, as long as they're not worn out. Apply Dexron, allow it to soak in a few minutes, and put it back into service. Come back a week later, wipe off the chains, and all the rust is gone. The chains look like new. It does a good job of removing rust.
I have a big derusting project ahead of me. A friend of mine gave me a Champion #40 forge blower. It's been outside. It's seized. I'm going to use a 55 gallon plastic drum as an electrolytic rust removal tank. One tablespoon of washing soda per gallon of water, a lot of water, a manual car battery charger, and a long piece of rebar. Throw about 6-10 amps to it and it will remove rust without changing the dimensions.