I use Fairy Power Spray or Mr Muscle Oven Cleaner. It's safe on plastics, resin and metal. Soak the models in a jar of the stuff overnight, then scrub with an old toothbrush. You may need to soak them again for an hour or 2 before another scrub.
Wear gloves while handling the stuff as it will dry out your skin and make it all flaky otherwise.
After the paint is off, just a quick rinse with water and towel dry them.
It may take longer to strip than using brake fluid but it's easier to dispose of the stuff. Brake fluid has to be taken to special places, you can't just pour it away down the drain.